Introduction to Bloodstain
Pattern Analysis
The Basics
14
14.1 Introduction
The purpose of this chapter is not to create Bloodstain Pattern analysis (BPA) experts but,
instead, to introduce students and novice scene scientists/investigators to the topic.
Hopefully, using this as a base, they will recognize critical patterns when they encounter
them and document them properly so that the potential value of the evidence is not lost.
The take-home lesson of this chapter is that the most inexperienced student or novice
scene scientist/investigator should realize that no bloodstain pattern should be overlooked
or go undocumented photographically and possibly videographically. Sketching is not a
satisfactory method to document bloodstain patterns except to show where they are and to
record their breadth and width.
Like glass, blood evidence can provide investigators with a range of investigative information. Some data that can be gathered from blood evidence were discussed in Chapter 13
and some are considered below.
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Origin/source of blood at the scene (i.e., whose blood?)
Distance from a target
Direction of travel
Energy of impact
Handedness
Relative position and movement of victim and assailant
Minimum number of blows
Sequence of events
Each of the above is a topic worth considering in more depth, and its forensic value
should be understood by students and scene scientists/investigators. Chapter 13 discusses
what some consider the most important reason for finding, collecting, and preserving
blood evidence at the scene—DNA. It can determine the presence of someone, to the exclusion of everyone else, at a scene. For this reason, blood and the patterns it forms—blood
evidence—must never be overlooked or considered lightly during an investigation.
Knowing whose blood made a particular pattern is important. Understanding how the
pattern formed can also provide a critical piece of investigative information. Learning
whose blood was where at the scene takes time, but BPA can be done on the spot. For
examining and analyzing blood evidence, the following two factors should be considered:
(i) Whose blood it is, and (ii) the circumstances of blood deposition.
The latter category—the circumstances of blood deposition—consumes the remainder
of this chapter simply because bloodstain patterns can be more valuable for the investigation
or to the medical examiner than knowing whose blood it is. Sometimes, there is no doubt
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about whose blood it is, simply by understanding the pattern and its location. Other than
the first in the list of eight reasons, the others refer to more esoteric questions concerning
how and why the blood ended up where it was.
Like the scene investigation itself BPA at the scene is deceptively easy. So, before considering the topic in more detail, it might be helpful to present, arguably, the historical
presence and growth of BPA into the criminal justice system and specifically law enforcement in the United States. This is a different discussion from the traditional historical
account where each investigator’s contribution to the field is considered in some depth. The
traditional historical account has been considered by others [1,2].
14.2 Historical Perspectives: BPA in the United States
The premise of bloodstain pattern analysts (agencies)* is that when blood leaves the human
body or a blood-covered object, it produces interpretable patterns. Bloodstains patterns
occur in multiple scene types, and investigators expect to find them at scenes of violent
crimes and suicides. Interpreting these patterns reliably depends on the training and experience of the individual analyst. While not a new discipline, much like crime scene investigation in general, BPA has attracted individuals having diverse educational and
professional backgrounds. Such diversity seems shocking for a discipline supposedly having a basis in science [4]. Shouldn’t science be practiced by scientists? The NAS report [5]
questions the scientific basis of pattern evidence, including BPA, because conclusions are
seemingly based more on experience than on scientific principle, even if the underlying
basis of the conclusions is science-based.
Much of forensics—as defined in Chapter 1—is an amalgamation or partnership of
forensic scientists and law enforcement professionals participating cooperatively in the
American criminal justice system: one is the scientist and the other the investigator. Crime
scene investigation is likely the largest subdiscipline of forensics where science is practiced
mostly by nonscientists and scientists, each often performing the same function. Certainly,
BPA belongs in that paradigm. This explains why lay investigators, who also perform
science at the scene, quickly adopted BPA as an investigative purview.† Criminalists who
participate in scene investigations also embraced BPA. It might be interesting to trace how
such a diverse group of professionals became so entrenched in the BPA arena.
Arguably, this began in the United States at the University of California Berkley with
the work of Dr. Paul Kirk, a well-known and respected forensic scientist. Dr. Kirk was hired
to investigate the 1950s murder of Dr. Sam Sheppard’s wife. Sheppard was arrested and
convicted of the crime. He claimed that an intruder entered his house and murdered his
wife. Dr. Kirk went to the scene, and wrote a brief concerning what he considered evidence
of someone else at the scene [7]. A book written by Sheppard’s son, Sam Reese Sheppard,
and attorney Cynthia Cooper, Mockery of Justice: The True Story of the Sam Sheppard Murder
Case [8], produced DNA evidence suggesting that Kirk’s interpretation was correct. Kirk’s
work in the case has become a legendary example of BPA. Interestingly, Kirk’s work went
seemingly unnoticed by police officials and crime scene investigators for some reason.
* Agency: ―. . . an individual, a law enforcement department, a private company, or a government or private
laboratory . . . that provides BPA as one of its functions‖ [3].
† Purview: ―the range or limit of authority, competence, responsibility, concern, or intention‖ [6].
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Perhaps, law enforcement did not agree with his interpretations. Perhaps, it considered his
work esoteric and beyond the skills of lay professionals.
The next important work in this area was a booklet by Herbert MacDonell and
L. Bialousz, Flight Characteristics and Bloodstain Patterns of Human Blood [9]. MacDonell’s
experiments and those he borrowed from other investigators—for example, the work of
Balthazard et al. in 1939 [10]—caught the attention of law enforcement. MacDonell began
offering workshops designed to train law enforcement officers how to interpret bloodstain
patterns, the result being a proliferation of individuals working on BPA cases throughout
the world. Importantly, the simplicity of these workshops spawned a cadre* of self-styled
experts who offered workshops of their own, and published books and articles. Criminalists
were also attracted to the discipline, much like they are to crime scene investigation.
MacDonell’s workshops and those that followed presented BPA in an easy-to-follow,
lively and fun format, which was and continues to be nonrigorous. Initially, there were no
written examinations or other traditional grading mechanisms, which meant failing was
not on the cards. In a sense, these workshops were like modern infomercials. Everyone who
completed the workshop received a certificate of attendance, giving many a sense of expertise. In a sense, then, by requiring not much more other than completing a week-long
course, attendees left with the feeling that BPA was simple enough to practice.
Recognizing the need for a formal organization around which the growing hoard of
BPA analysts could communicate, MacDonell was instrumental in establishing the
International Association of Bloodstain Pattern Analysts (IABPA), founded in 1983 [12].
On-going workshops and a growing membership in the IABPA resulted in the continued
proliferation of lay investigators, many having dubious scientific and/or investigative credentials, who performed BPA in casework for both sides of the adversarial system. Their
opinion testimony has played a critical role in determining innocence or guilt.
The books, newsletters, and articles until recently have been geared to a law enforcement audience. These are uncomplicated. They use easy to understand, with nonscientific
terminology. Some of the more recent publications are more scientific in nature, as shown
in a recent IABPA newsletter [13].
The International Association of Investigators (IAI) initially considered BPA a part of
its crime scene certification. At the time of this writing, the IAI made BPA its discipline
and is now certifying individuals who meet its requirements. Although the 2009 NAS
report [5] questions the scientific basis of BPA, practitioners dispute this, and Scientific
Working Group on Bloodstain Pattern Analysis (SWGSTAIN) put together an extensive
bibliography of relevant articles to counter possible legal challenges to BPA [14]. Even
before the NAS report was published, however, Laber et al. [15] working in the Minnesota
crime laboratory who have been active in bloodstain pattern research and education wrote
that BPA is a scientific endeavor. The following quote was taken from the introduction and
conclusion of their article, which preempted the NAS report. They warned BPA analysts
to move quickly to strengthen the discipline. Concerning the dynamics of how blood
patterns form, they wrote [15]:
Relatively little however, has been documented about the dynamics of the blood transfer
event. . .. BPA is a discipline that has relied heavily on the experience of the witness . . . closer
* Cadre: ―a nucleus or core group especially of trained personnel able to assume control and to train others ;
broadly: a group of people having some unifying relationship‖ [11].
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scrutiny of the methods used in BPA will highlight the relative lack of underpinning scientific
research and validation studies. (pp. 4, 11) [Emphasis added.]
As the number of cases involving BPA and the number of analysts increased, it became
clear that standards were needed. In 2002, the FBI began sponsoring a professional group
devoted to BPA, the SWGSTAIN, whose mission is:
. . . to serve as a professional forum in which BPA practitioners and practitioners from related
fields can discuss and evaluate methods, techniques, protocols, quality assurance, education,
and research relating to BPA [16,17].
SWGSTAIN began formulating guidelines for practicing BPA. The logical place to
begin was to standardize BPA terminology [18] in order to create a mechanism for communicating. Another benefit was to eliminate the confusing terminology resulting from
individuals who had published works on their own in the absence of a standard. Interestingly,
the SWGSTAIN final version was not published until after publication of the NAS report
in 2009. Before SWGSTAIN published its terminology, authors recognized how complicated BPA patterns could be and began introducing their own terminology. A few examples
will suffice to illustrate the point: Bevel and Gardner [1] use a classification system where
the main categories are the Spatter Family, the Non-Spatter Family, and Complex Patterns;
James et al. [19], in their terminology, include the categories of Passive, Spatter, and Altered;
and Wonder [20] provides a flow diagram to assist in classifying bloodstain patterns where
the main categories are Spatter Groups, Spatters Not a Criteria, and Composites. For now,
SWGSTAIN’s terminology is a welcome attempt at standardization. Importantly, it offers
a terminological playing field from which BPA analysts and novices can communicate.
Table 14.1 has been adapted from the terminology listed on the SWGSTAIN Web site
[18]. No photographs are associated with the table, but some examples are in the text and
the Internet also has examples. Some are for the IABPA terminology [21]. The same Web
site also lists the new SWGSTAIN terminology [22]. Laber et al. [15] filmed blood patterns
as they formed (see also the MFRC Web site [23]).
14.3 Scientific Basis of BPA
If BPA has a basis in science, then testimony at trial should be admitted into evidence as
long as the testifying expert analyst meets appropriate standards and has the appropriate
credentials. So, what criteria should a competent BPA analyst meet? The BPA expert should
understand the physics and mathematics relating to BPA. This understanding is gained
through education and experimentation with blood while applying the principles of the
relevant scientific disciplines: biochemistry, fluid mechanics (dynamics), physics, chemistry, ballistics, and mathematics. These disciplines form the scientific basis of BPA, and their
principles must be able to explain why blood forms the patterns it does. If they cannot, then
BPA does not have a basis in science and must be considered under the arts.
As the NAS report implies, someone’s life depends on the reliability on the opinion of
someone whose sole basis for that opinion is experience. This does not imply that BPA has
no scientific basis or that the opinions rendered in court are incorrect. The scientific basis,
although probably solid, must be proven: SWGSTAIN provides references designed to
document the scientific basis of BPA [14]. The following discussion is designed as an
overview of the disciplines relevant to BPA.
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Table 14.1 2009 Recommended SWGSTAIN BPA Terminology
Terminology
Accompanying drop
Angle of impact
Altered stain
Definition
A small blood drop produced as a by-product of drop formation.
The acute angle (alpha), relative to the plane of a target, at which a blood
drop strikes the target.
A bloodstain with characteristics that indicate a physical change has
occurred.
Area of convergence
The area containing the intersections generated by lines drawn through the
long axes of individual stains that indicates in two dimensions the location
of the blood source.
Area of origin
Backspatter pattern
The three-dimensional location from which spatter originated.
A bloodstain pattern resulting from blood drops that traveled in the opposite
direction of the external force applied; associated with an entrance wound
created by a projectile.
A gelatinous mass formed by a complex mechanism involving red blood cells,
fibrinogen, platelets, and other clotting factors
A deposit of blood on a surface.
A grouping or distribution of bloodstains that indicates through regular or
repetitive form, order, or arrangement the manner in which the pattern was
deposited.
Blood clot
Bloodstain
Bloodstain pattern
Bubble ring
Cast-off pattern
Cessation cast-off pattern
Directionality
Directional angle
Drip pattern
Drip stain
Drip trail
Edge characteristic
An outline within a bloodstain resulting from air in the blood.
A bloodstain pattern resulting from blood drops released from an object due
to its motion.
A bloodstain pattern resulting from blood drops released from an object due
to its rapid deceleration.
The characteristic of a bloodstain that indicates the direction blood was
moving at the time of deposition.
The angle (gamma) between the long axis of a spatter stain and a defined
reference line on the target.
A bloodstain pattern resulting from a liquid that dripped into another liquid,
at least one of which was blood.
A bloodstain resulting from a falling drop that formed due to gravity.
A bloodstain pattern resulting from the movement of a source of drip stains
between two points.
A physical feature of the periphery of a bloodstain.
Expiration pattern
A bloodstain pattern resulting from blood forced by airflow out of the nose,
mouth, or a wound.
Flow pattern
A bloodstain pattern resulting from the movement of a volume of blood on a
surface due to gravity or movement of the target.
A bloodstain pattern resulting from blood drops that traveled in the same
direction as the impact force.
Forward spatter pattern
Impact pattern
Insect stain
Mist pattern
Parent stain
Perimeter stain
Pool
A bloodstain pattern resulting from an object striking liquid blood.
A bloodstain resulting from insect activity.
A bloodstain pattern resulting from blood reduced to a spray of micro-drops
as a result of the force applied.
A bloodstain from which a satellite stain originated.
An altered stain that consists of the peripheral characteristics of the original
stain.
A bloodstain resulting from an accumulation of liquid blood on a surface.
continued
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Table 14.1 (continued) 2009 Recommended SWGSTAIN BPA Terminology
Projected pattern
A bloodstain pattern resulting from the ejection of a volume of blood under
pressure.
A smaller bloodstain that originated during the formation of the parent stain
as a result of blood impacting a surface.
A bloodstain resulting from the accumulation of liquid blood in an absorbent
material.
Satellite stain
Saturation stain
Serum stain
The stain resulting from the liquid portion of blood (serum) that separates
during coagulation.
A bloodstain resulting from a blood drop dispersed through the air due to an
external force applied to a source of liquid blood.
A bloodstain pattern resulting from a volume of liquid blood that falls or
spills onto a surface.
Spatter Stain
Splash pattern
Swipe pattern
A bloodstain pattern resulting from the transfer of blood from a bloodbearing surface onto another surface, with characteristics that indicate
relative motion between the two surfaces.
Target
Transfer stain
Void
Wipe pattern
A surface onto which blood has been deposited.
A bloodstain resulting from contact between a blood-bearing surface and
another surface.
An absence of blood in an otherwise continuous bloodstain or bloodstain
pattern.
An altered bloodstain pattern resulting from an object moving through a
preexisting wet bloodstain.
Source: Adapted from FBI, Scientific Working Group on Bloodstain Pattern Analysis: Recommended terminology. Forensic Science Communications, 11(2), 2009. Available at: http://www2.fbi.gov/hq/lab/fsc/
backissu/april2009/standards/2009_04_standards01.htm.
14.3.1 Biochemistry
To address the topic properly, one must understand the nature of blood, which requires
knowledge of biochemistry and physics. As described in Chapter 13, blood is a tissue, a
liquid/solid suspension of plasma and cells. The liquid fraction (plasma) is a water-based,
complex mixture of dissolved proteins, salts, and other molecules. The solid fraction contains a variety of cell types. Thus, blood is classified as a viscoelastic* [24] non-Newtonian
fluid† [25]. And understanding what happens to it after it leaves the human body, whether
acted upon by a force or just passively dripping from an object, requires more than empirically observing how bloodstains form in a workshop setting or in the field.
*
†
Viscoelastic: ―having appreciable and conjoint viscous and elastic properties‖ [24].
Non-Newtonian: ―fluid whose flow properties differ in any way from those of Newtonian fluids. Most
commonly the viscosity of non-Newtonian fluids is not independent of shear rate or shear rate history.
However, there are some non-Newtonian fluids with shear-independent viscosity, that nonetheless
exhibit normal stress-differences or other non-Newtonian behavior. Many salt solutions and molten
polymers are non-Newtonian fluids, as are many commonly found substances such as ketchup, custard,
toothpaste, starch suspensions, paint, blood, and shampoo. In a Newtonian fluid, the relation between
the shear stress and the shear rate is linear, passing through the origin, the constant of proporti onality
being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the
shear rate is different, and can even be time-dependent. Therefore a constant coefficient of viscosity cannot
be defined‖ [25].
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14.3.2 Physics
The laws of physics apply to blood droplets in flight. Fortunately, physics is a well-studied
and documented discipline, and the direct application to blood droplet formation and its
flight characteristics should be understood. The problem for BPA is that these considerations have been taken for granted and, aside from empirical studies in workshop settings,
few publications exist documenting that blood flight conforms to these laws. Certainly, one
would expect that it does. The following sections examine briefly physics-related disciplines relevant to blood droplet movement.
14.3.2.1 Surface Tension
Blood plasma is composed of macromolecules, namely proteins and carbohydrates, and
water and other dissolved salts and molecules. Its physical properties—viscosity and surface tension—are mainly determined by dissolved macromolecules in the blood’s plasma.
Surface tension* is a force that forces blood droplets (or any liquid) to maintain its integral
structure, retain its shape, until acted on by a force greater than the force of surface tension. It is this force that creates blood spatter and thus the patterns observed at crime
scenes. In the strictest sense, how the force is applied, its strength, determines the visual
appearance of the resulting pattern.
14.3.2.2 Fluid Mechanics (Dynamics)
Fluid mechanics is the study of fluids (liquids, gases, and plasmas) and the forces that act
on them.† Thus, its laws define blood in motion after being acted on by a force. Fluid
mechanics, either fluid statics (fluids at rest) or fluid kinetics (fluids in motion), is a
branch of continuum mechanics, which considers matter (including blood) as models
in a continuum rather than as discrete atoms. Using fluid dynamic computations to
describe blood in motion, for example, bloodstains formed from impact spatter, is particularly relevant. Typically, these computations fall into the purview of scientists who
practice computational fluid dynamics.‡ The bottom line is that every drop of blood (or
perhaps pattern of blood) at the crime scene can and perhaps should be described mathematically. Some publications exist, but such a comprehensive study has not been done
systematically.
14.3.2.3 Trajectory Analysis (Ballistics)
When a blood droplet leaves the human body under a force, it forms an arc, a path described
mathematically. The droplet represents a projectile and its path is its trajectory. Much like
Surface tension: ―the attractive force exerted upon the surface molecules of a liquid by the molecules
beneath that tends to draw the surface molecules into the bulk of the liquid and makes the liquid assume
the shape having the least surface area‖ [26]
† Fluid mechanics: ―a branch of mechanics dealing with the properties of liquids and gases‖ [27]. According
to Wikipedia, ―Fluid mechanics is the study of fluids and the forces on them. (Fluids include liquids,
gases, and plasmas.) Fluid mechanics can be divided into fluid kinematics, the study of fluid motion, and
fluid dynamics, the study of the effect of forces on fluid motion, which can further be divided into fluid
statics, the study of fluids at rest, and fluid kinetics, the study of fluids in motion‖ [28].
‡ Computational fluid dynamics (CFD): ―branch of fluid mechanics that uses numerical methods and
algorithms to solve and analyze problems that involve fluid flows‖ [29].
*
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391
a bullet, the shape of the arc a blood droplet takes to its terminus depends on gravity, wind
currents, temperature, humidity, and friction. In the absence of these external influences,
the arc described by the blood droplet’s path would be a parabola defined by a uniform,
homogeneous gravitational force field. In the real world, such a singular effect is nonexistent. Air resistance (friction), drag, and nonuniform gravitational forces exert their influence on the path. So, in the real world, the path the droplet takes is not a true parabola, its
trajectory reflecting the influences of drag and gravity.
14.3.2.4 Gravitation (Gravity) *
Gravity is one of the four fundamental interactions of nature (which include strong and
weak interactions, electromagnetism, and gravitation) where objects having mass attract
one another [31]. Described by the general theory of relativity, it is a consequence of the
curvature of space time that governs the motion of inertial objects and causes dispersed
matter to coalesce, such as when the earth and other planets formed after the Big Bang. It
is also the force that causes objects to fall to the ground when dropped. It keeps the planets
in their obits around the sun and the moon around the earth. Gravity’s influence on blood
droplets was mentioned earlier as affecting a droplet’s trajectory (path) because it defines
the path an object (blood droplet) takes (nongravitational influences such as drag not considered) until it finds its terminus. Thus, gravity is responsible for the natural consequence
of fluid flow. Its influence is starkly apparent in the visual pattern of spattered blood at
scenes as well as its pooling and flow.
14.3.2.5 Terminal Velocity
One area of study of BPA concerns the concept of terminal velocity, also a concept of
fluid dynamics. A blood droplet reaches its terminal velocity (settling velocity) when its
acceleration due to the downward force of gravity equals the upward force of drag. When
a blood droplet’s speed is constant, drag equals the droplet’s weight, and its acceleration
is zero. For bloodstains falling from identical heights and having a constant weight
(volume), their terminal velocities will be identical. Similarly, when a blood droplet reaches
its terminal velocity, the resulting stain, say on a hard flat surface, will have a constant
diameter, regardless of the height from which it falls. Generally, terminal velocity occurs
at approximately 20 ft, but empirical experiments (in workshops) show that bloodstain
diameters change very little after falling approximately 7 ft (see p. 21 in Ref. [2]). This is
illustrated in Figure 14.1, taken from the work by James and Eckert [2]. The
cardboard, onto which the droplets fell, although smooth, had some texture as evidenced
by the formation of spines coming off of the parent drop and satellite droplets surrounding
the parent drop. The scalloping edge characteristics of the droplets are also indicative of a
textured surface.
* Gravity: ―the gravitational attraction of the mass of the earth, the moon, or a planet for bodies at or near
its surface (2) : a fundamental physical force that is responsible for interactions which occur because of
mass between particles, between aggregations of matter (as stars and planets), and between particles (as
photons) and aggregations of matter, that is 10 −39 times the strength of the strong force, and that extends over
infinite distances but is dominant over macroscopic distances especially between aggregations of matter—
called also gravitation, gravitational force‖ [30].
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6 in
1 ft
2 ft
3 ft
4 ft
5 ft
6 ft
7 ft
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Single drops of blood falling onto smooth
cardboard from various heights.
Little change in diameter beyond 7 ft. Used with permission.
Figure 14.1 Height versus droplet stain diameter.
14.3.2.6 Centripetal Force
When wet blood is cast off a moving object (a weapon, hands, etc.), only one force is at
work, centripetal force.* This is a force directed toward the center of the path of the moving
object. When the adhesive forces holding the blood onto the object are greater than the
centripetal force, the blood will fly off the object tangentially in a straight line. The resulting impact site is a direct link to the location of the object at the precise moment the blood
left the object. The centripetal force should not be confused with centrifugal force,† which
is a perceived force that does not exist. Blood cast off a weapon is an example of centripetal
force (see Section 4.2.3.7).
14.4 Fundamental Principles of BPA
Empirical work has identified areas of BPA that many consider fundamental. These include
the direction of movement of a bloodstain and the angle of impact, that is, the angle at
which blood droplets strike a surface. Other fundamental characteristics affecting resulting
bloodstain include shape, volume, and so on.
14.4.1 Blood Droplets and Surface Tension: Shape of a Falling Droplet
Foundational research by Pizzola et al. [34,35] helped define the property of blood in
motion by documenting widely held beliefs about how blood droplet patterns form. Their
work confirmed that the principle of fluid dynamics does apply to blood droplets in motion.
This had been suspected but not proven. They demonstrated photographically how surface
tension affects falling droplets, as illustrated in Figure 14.2.
When blood drips from an object, whether passively or actively (bleeding wound),
it accumulates at the leading edge of the object until so much is there that its weight
* Centripetal force: ―the force that is necessary to keep an object moving in a curv ed path and that is
directed inward toward the center of rotation <a string on the end of which a stone is whirled about exerts
centripetal force on the stone>― [32].
† Centrifugal force: ―the apparent force that is felt by an object moving in a curved pat h that acts outwardly away from the center of rotation‖ [33].
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Blood–covered
pointed weapon
Blood accumulates until
droplet weight > gravity
Surface tension pulls
vertically & horizontally
to keep droplet together
Droplet settles
into a sphere
Figure 14.2 Effect of surface tension on the shape of blood droplets.
overcomes the force of gravity. Then, the droplet leaves the surface and begins to fall and
accelerates until it reaches its terminal velocity. At first, its shape is flattened (top photograph in the sequence in Figure 14.2). The surface tension pulls vertically and horizontally
to keep the droplet together, eventually resulting in a spherical shape.
14.4.2 Defining the Direction of Blood Travel
14.4.2.1 Shape of Blood Droplets after Striking Surfaces
Eckert [36] illustrated what bloodstains should look like after striking a sloped surface
(falling directly downward at 90°)—top left of Figure 14.3—it forms a circle, and, depending on the texture of the surface (smooth, textured, dusty, etc.), its edge characteristics
exhibit varying amounts and intensity of scalloping. As the impact angle becomes more
and more acute, the stain elongates, eventually forming a tail—bottom right of Figure 14.3,
which points toward the direction the blood droplet was traveling. Examining the tail is an
easy way to determine the direction in which the blood droplets are moving. In Eckert’s
[36] experiment, blood droplets were dropped onto a hard surface and then photographed.
Most BPA workshops have students work through a set of experiments that empirically
demonstrate the shape blood takes as it hits surfaces at various angles. Students are asked
to perform the experiment and to calculate the angle of impact (Workshop VI-1).
14.4.2.2 Dynamics of Blood Striking Angle d Surfaces
Pizzola et al. [34,35] showed what happens to blood when it strikes an angled surface. The
snapshots of their video clearly demonstrate the process of droplet touch to expansion to
tail formation. Their work is shown in Figure 14.4.
14.4.2.3 Blood or Drip Trails
According to the SWGSTAIN terminology [18] discussed earlier, a drip trail is, ―A bloodstain pattern resulting from the movement of a source of drip stains between two points.‖
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Figure 14.3 Shape of blood after striking surfaces at various angles. Used with permission
Figure 14.4 Snapshots of high-speed video of blood droplet hitting angled surface. (Adapted
From P. A., Pizzola, S., Roth, and P. R., Deforest, Journal of Forensic Sciences , 31(1):50–64, 1986.) Used
with Permission.
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When blood drips from an object in motion, the resulting droplet shapes can range from
nearly circular (falling nearly perpendicular to the surface) to elongated (hitting the surface
at an angle) depending on the speed of the travel. If the droplets form elongated stains,
determining the direction of travel is a simple matter of seeing which direction the stain
points (see Section 5.1.2). However, for blood dripping from slowly moving objects, such
as from someone walking with a bleeding wound, the droplets can be nearly circular and
mimic droplets falling vertically from a height. An example of a drip trail is shown in
Figure 14.5. Arrows show three droplets in the trail.
Determining the direction of these stains depends on closely examining edge characteristics, and this very much depends on the texture of the interacting surface—that is,
how smooth it is. Generally, the edge characteristics of droplets in motion point in the
direction in which the droplet is traveling, which in most circumstances would be the
direction in which the person is moving. Depending on the texture of the interacting
surface, the leading edge (the edge in the direction of travel) will be more or less uneven,
that is, it can have scalloping, spines, and/or satellite stains. On extremely smooth surfaces, the edge characteristics of the droplet are minimal or nearly nonexistent. On textured surfaces, edge characteristics are rough, that is, they exhibit scalloping and could
have spines or satellite stains. When the edge characteristics are prominent, they are
diagnostic of the direction in which someone who was bleeding, for example, was
moving.
Relying on a single droplet in a drip trail to determine the direction of movement is a
mistake, however, and can lead to misinterpretation or confusion. Figure 14.6 is an example of a droplet stain from a bleeding hand of someone who was walking. It has, at first
glance, the appropriate diagnostic edge characteristics: scalloping on the left, suggesting it
Figure 14.5 Drip trail. (Photograph by Robert C. Shaler.)
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Figure 14.6 Blood droplet in blood drip trail. (Photograph by Robert C. Shaler.)
originated from someone moving from right to left. On closer inspection, however, edge
scalloping is also present on the right edge—in the lighter area in Figure 14.6. Interpretation
of such edge characteristics can be confusing because the blood has concentrated on the
left side of the droplet suggesting that it lies on a floor slanting left. In truth, the floor is
horizontal, and the lighter clear area resulted from the aqueous droplet being repelled by
wax on a freshly waxed floor. Closer inspection of the light area shows scalloping and small
satellite stains, the latter suggesting movement from left to right. This is the correct interpretation, and interpreting the droplet as moving from right to left would have been incorrect. If other stains in the trail were equally as confusing as the stain shown in Figure 14.6,
the logical interpretation should be inconclusive.
On highly textured surfaces, such as a wooden porch, scalloping, spines, and satellite
stains are common, and determining the direction of travel is relatively straightforward.
But even under these circumstances, using a single stain to determine the direction of
travel is prone to error. For example, if a droplet hits a particularly rough area, it could
result in edge characteristics on all sides of the droplet stain. Again, choosing several stains
is the proper technique for determining the direction of travel of a blood trail.
14.4.2.4 Shape and Size of Bloodstains
The shape of bloodstains is dependent not only on the angle at which it impacts the surface
but also on the characteristics of the surface it impacts: texture, absorptive properties, and
thickness. Figure 14.7 shows blood droplet stains on T-shirt material (top photograph) and
on a thick, absorptive cotton towel (bottom photograph). Generally, the rougher the surface the greater its texture and the more disrupted the resulting droplet stain will appear.
In the upper stain, on T-shirt material, the edge of the stain is irregular, spines are apparent, and so is a satellite droplet stain, all misshapen due to the texture of the material. The
bottom stain is a droplet of the same volume and dropped from the same height as that on
the T-shirt material. This is a highly absorptive, thick cotton towel, and the shape of the
droplet stain is decidedly different from that on the T-shirt material.
The diameter of a droplet stain depends not only on the volume of the droplet but also
on the absorptive properties of the surface. If the surface absorbs liquids readily and is
thick enough, the appearance of the stain tends to be compact, reflecting the ability of the
surface to absorb the blood quickly and deeply into its matrix (the lower photograph in
Figure 14.7). By contrast, if the surface is highly absorbent but thin, the resulting stain
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Crime Scene Forensics
Shape & size of
bloodstain droplets
 Shape v. target surface
 Texture (rough or smooth)
Affects shape of droplet
Collisions with surfaces that
are not flat
 Size

Distance fallen
Little change in diameter
beyond 8 feet

Absorptivity/porosity
More absorptive, better
spreading of droplet into
surface

Thickness
Thick, absorptive surface pulls
droplet into matrix & keeps
from spreading
–
–
–
–
–
Figure 14.7 Effect of surface absorption on shape and size of bloodstains. (Photograph by
Robert C. Shaler.)
spreads out quickly because the lack of depth in the fabric wicks the blood away from the
impact site (the top photograph in Figure 14.7). The volume of the two droplets shown in
the photographs was identical. The edge of the stain in the bottom photograph is irregular,
but there are no spines or satellites. Presumably, the absorptivity of the towel interrupted
the ability of the textured surface to overcome the surface tension by quickly absorbing the
droplet into the towel’s matrix.
Figure 14.8 illustrates how the texture of the surface affects the appearance of the
resulting stain, minus the absorptive effect discussed above. All four photographs in this
figure are of blood droplets dropping onto a nonporous surface. The top two photographs
Surface characteristics & droplet shape
Single droplets falling onto various surfaces
400 Grit
sandpaper
Droplet on wood
150 Grit
sandpaper
Droplet on velcro
Figure 14.8 Effect of surface texture on the shape of bloodstains. (Photograph by Robert C.
Shaler.)
Introduction to Bloodstain Pattern Analysis
397
illustrate how sandpaper grit (roughness)—400 (smoother) and 150 (rougher)—affects the
appearance of the resulting stain. The general rule of thumb is that the rougher the surface,
the more disrupted the resulting stain. The 150 grit sandpaper is rougher and disrupts the
droplet more than one falling onto a piece of the smoother, 400 grit sandpaper. In each
case, the same volume of blood fell from the same height. Each droplet stain has spines and
satellite stains are apparent (arrows). The stain on the 400 grit sandpaper clearly shows its
scalloped edge while the stain on the 150 grit sandpaper is so badly disrupted that the scallops are not visible.
The lower left photograph in Figure 14.8 shows a stain produced from a droplet impacting
a piece of wood. The surface texture of the wood disrupts the droplet as much as the 150 grit
sandpaper (upper right). The lower right photograph shows what happens to a droplet falling
onto the hooked side of Velcro, the blood being wicked along the hooks (right and left) giving
an unusual stain with elongated spines. Satellite stains are also visible (arrow).
14.4.2.5 Perimeter Stain: Ghosting or Skeletonization
When a blood droplet hits a surface or is transferred to it after wiping against it, the blood
is still wet. Over time it will dry. The drying process moves from the outside toward the
inside. This happens because the outside edges of the droplet are shallower and lose their
water quicker than the middle of the droplet which is thicker. Therefore, as the stain dries,
its edges dry quicker. If someone or something brushes across the drying droplet, the edges
form an outline of the original droplet (see arrows in Figure 14.9).
14.4.2.6 Calculating the Angle of Impact
Understanding the mechanism of why blood forms elongated stains as the angle at which
it strikes becomes increasingly small is critical in understanding how to determine the
angle at which the blood impacted with the surface. As mentioned earlier, Pizzola et al.
[34,35] demonstrated photographically how elongated patterns form. Though BPA analysts
had been calculating impact angles for decades before their work was published, they confirmed and validated BPA analysts’ use of trigonometric functions.
Figure 14.10 is adapted from MacDonell and Bialousz’s [37] geometric model for
calculating the impact angle. When a blood droplet hits a surface it forms a right triangle
Figure 14.9 Ghosting or skeletonization. Photography by Ralph Ristenbatt III. Used with Permission.
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Crime Scene Forensics
d
Blood
droplet
B = Angle
of incidence
Vertical
drop
Right
angle
A=Angle
of impact
A
A
Stain
B
D
Surface
Stain diameter is generally greater than the droplet diameter : (D > d)
Figure 14.10 Droplet size versus stain size. (Adapted from H. L. MacDonell, and L. Bialousz,
Laboratory Manual on the Geometric Interpretation of Human Bloodstain Evidence , Laboratory
of Forensic Science, Corning, NY, 1973.)
(illustrated in the left diagram in Figure 14.10), whose angle ―A‖ can be calculated using
trigonometric functions. The mechanism for why this type of calculation is correct is illustrated on the right. The step-by-step procedure for measuring a stain prior to making the
calculation is listed below.

Approximate the outline of the stain as shown in the slide on the right in Figure
14.10— white oval. Do not include the stain’s tail (E) in the approximation.

Measure the length (D) and the width (d) from the stain. Calculate the fraction
by dividing the width by the length (d/D) (Figure 14.11).

Calculate the impact angle by taking the arc sine (sin −1) of the fraction
(d/D). A fraction of 0.5 represents a 30° angle.
Significant error is built into calculating the impact angle, which arises from measurement error, error in selecting an appropriate stain (the more elongated the stain, the less
Point of contact
with surface
Procedure
Measure length L
Measure width W
Calculate ratio W/L
Calculate arc sin W/L
Figure 14.11 Calculating the angle of impact.
W
L
of
Direction
of droplet
travel




Introduction to Bloodstain Pattern Analysis
399
the error; the more circular the stain, the greater the error), and surface characteristics that
distort the stain by differential absorption or other surface characteristics. Error rates can
be quite high and can range from 1%–2% to over 20%, with an average of approximately
5%. Recent publications [38,39] have targeted errors in calculating impact angles using
more rigorous mathematical methods.
14.4.2.7 Determining the Origin of an Impact
Knowing how to determine the angle of impact, the angle at which a blood droplet struck
a surface, is the first step in determining the area of convergence of a number of blood
droplets that originated from a single source.
14.4.2.7.1 Point of Convergence or Back Projection in Two Dimensions The point of
convergence represents the 2D location of an impact, such as what happens in blunt force
trauma when someone is beaten with an object or a fist. Importantly, for blood to be spattered, it must be present, which means that a first impact occurred in order to produce
blood. The back projection approach is helpful in determining a possible minimum number
of blows or impacts (impact spatter cannot occur until blood is present to be splashed).
Multiple points of convergence suggest multiple blows. This is also a mechanism for selecting the proper bloodstains from within a bloodstain impact spatter pattern to use in determining the 3D area of impact. Figure 14.12 illustrates the process.
The procedure outlined in Figure 14.12 lists the steps necessary to determine the 2D
point of impact. After determining the direction of travel (blood points in the direction in
which it was moving), back project a line through the axis of the blood droplet stain. Repeat
this procedure for several droplets (as many as 20 per impact pattern). The point (or general area) where they meet is the 2D point of convergence. This represents:


The 2D point of impact of at least one impact.
The point of impact of more than one impact, if the multiple impacts had the
same precise spatial location.
Determining 2D points(s) of convergence
2D point of
convergence
Multiple points of
convergence suggest
multiple actions
Procedure
 Determine direction of travel
 Back project through axis of Stain
 Determine 2D convergence point
Figure 14.12 Back projection method for point of convergence.
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Crime Scene Forensics
14.4.2.7.2 Area of Origin in Three Dimensions The spatial location of an impact that
caused impact spatter pattern can be important in piecing together a possible sequence of
events. Essentially, this is the third dimension of the 2D back projection shown above. If
the stain impact location can be determined in two dimensions, it is a simple matter of
converting that into a 3D image, accomplished using 3D imaging techniques, such as 3D
scene imaging systems, CAD programs or software specifically designed for the application. It can also be approximated at the scene using what is known as the string method,
manually or by lasers. Alternatively, the spatial area (point) can be calculated using a combined manual/trigonometric method. The steps for that process are listed below.
14.4.2.7.3 The Tangent Method

Use the stains as in the 2D back projection method discussed above. Back
project the stains to the point of convergence—Step 1 in Figure 14.13 was
illustrated in Figure 14.12.

Measure the width (W) and the length (L) of two droplet stains.

Calculate the impact angle by taking the arc sine of the width divided by the
length of the bloodstain.

Measure the distance from the point where the blood droplet hit the surface to the
point of convergence.

The height of the area of impact (Z) is calculated using the tangent function, as
shown in Figure 14.13.
14.4.2.7.4 The String Method The string method mentioned above is a manual procedure for
approximating the area of origin resulting from an impact. Generally, several appropriate
stains are selected (10–20 stains) from within a bloodstain pattern; sometimes determining the
best stains can be identified using the 2D back projection process first. An example of the
string method is shown in Figure 14.14. In the example, impact spatter was created to
recreate a stomping death, and a blood-soaked mock head was stomped several times. The
back projection method was used to identify appropriate stains (dark pencil lines
Tangent method
z = tan (impact angle) x length
?
3D area of impact
Z (height)
2D Pt. of convergence
2. Determine impact angle
using sin–1(d/D) function
1. Back
project
1. Back project
Figure 14.13 Tangent method to determine area of origin.
Introduction to Bloodstain Pattern Analysis
401
Figure 14.14 An example of the string method.
drawn through the axes of several bloodstains are visible on the walls). Next, the impact
angles were measured and strings run to the floor and anchored at those angles. The area of
impact is where the strings more or less converge. The imprecision of the area seen in the
photograph is related to multiple stomping actions, many of which were not in the same
precise location of the mock head but not so far removed so as to create multiple impact
areas.
Appropriate stains have the following specific characteristics:

They should be traveling linearly, which means they still posses most of the
energy imparted to them during the impact. The easiest way of determining which
stains are appropriate is to identify them from a back projection 2D analysis. As the
stains lose energy, they begin to arc and fall, and are of no use to the analyst trying
to determine the spatial origin of an impact.

Stains should be as elongated as possible, given the complexities of the
pattern analyzed. Measuring these stains is less prone to error than circular
stains.
14.4.2.7.4.1 Step-by-Step Procedure of the String Method

Depending on the quality of the pattern, choose as many as 20 elongated
stains that were traveling linearly from the impact point before striking the
surface. Number each stain chosen sequentially and tape that number to the wall
(surface) next to the stain. Record the information in a log.

Calculate the impact angle for each stain (arc sine width/length). Record the
angle in a log and also onto the piece of tape placed next to the stain on the
impact surface.

Tape the end of a long piece of string at the precise point where the blood
droplet hit the surface.

Ensuring the tape holding the string is secure and using a zero-edge
protractor, track the string through the center of the stain’s axis along the protractor
at the calculated impact angle. Pull the string taut and attach it to the surface, for
example, floor or other object. Recheck the measurements and the determined
stain trajectory (the string) to ensure the angle of the droplet impact is correct.
Repeat the process for as many as 20 stains in the pattern. If the pattern is from a
single event, if the appropriate stains were selected, if the measurements were
determined correctly, and if the string was run at the correct angle, the strings
should converge
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Crime Scene Forensics
Table 14.2 Troubleshooting String Method Problems
Reason
Correction Method
Poor stain selection
Incorrect stain measurement
Incorrect angle using the zero-edge
protractor
Multiple impacts occurring in the
same general spatial location
Re-examine the impact pattern and the stains selected.
Repeat measurements to ensure measurement accuracy.
If angles were calculated correctly (above), check the protractor
positioning. If placed correctly, recheck string positioning.
Use 2D back projections to determine whether multiple impacts
occurred. If so, use the 2D method to choose stains from each impact
and make overlapping 3D area of impact determinations.
in an area in space that approximates the area of the impact. If the area of
convergence seems too large, the process might not have been performed correctly.
Table 14.2 gives troubleshooting suggestions.
14.4.2.7.5 Cast-Off When blood leaves a blood-covered object it can either drip passively
or be propelled from it. In the forensic circumstance, blood leaves a blood -covered
object when the centripetal force acting on it overcomes the adhesive forces holding the blood
onto the object (Figure 14.15). This is true whether the blood cast from the object occurs
while the bloody object is being swung or if it comes to an abrupt halt (cessation cast-off).
If blood is on a bloody knife and the knife is swung in an arc, blood will be propelled
(cast off) the knife in a path that is tangentially straight from that point and travel until it
hits/impacts a surface. If blood hits the surface while still traveling in the straight line, the
shape it takes will represent the angle of the impact. Therefore, trigonometric functions
can be used to calculate its impact angle and also backtrack to the spatial location of when
it left the bloody object.
More than one droplet will usually leave the bloody object as it moves through its path,
the preponderance of which will form a pattern characteristic of the bloody object. These
characteristics are listed below.
• Surface area of the object facing the impact surface: Thus, if the bloody object is a
hand and the hand is sideways to the impact surface, say a wall, the cast-off pattern
formed represents that surface of the hand facing the impact. In this instance, it
Centripetal force
Directed toward the center of
the path of the moving object.
When adhesive forces holding
blood onto the object
overcome centripetal force, the
blood will fly off object in a
tangentially straight line.
The impact angle of the stain
is direct link to location of the
object at the exact time blood
left it.
Figure 14.15 Centripetal force and cast-off.
Movement of object
left-to-right
Introduction to Bloodstain Pattern Analysis
405
Figure 14.16 Cessation cast-off. Photograph by Robert C. Shaler
will be a broad line of individual droplets. As the hand moves through its arc, the
hand will change its position and, perhaps, individual fingers will now face the
wall. As this begins to happen, the cast-off pattern will broaden and might, at its
end, show the cast-off pattern from individual fingers.
• The breadth of the cast-off pattern: This reflects the blood-covered surface area of
the surface facing the impact site. Thus, a knife blade will often give a single line of
cast-off staining, while a baseball bat can give a broader cast-off pattern. If the
knife’s flat side of the blade is facing the impact area, the breadth of the cast-off pattern will reflect the width of the knife blade, although not its actual dimensions.
A unique type of cast off occurs when a bloody object comes to a rapid halt. This
can occur when a blood-covered weapon strikes a wall, a person, or some other object.
Figure 14.16 shows an example of a bloody knife falling to the floor. The yellow arrow
shows the direction of the movement of the object as it hit the floor.
14.4.2.7.6 Bubble Stains Bubble stains form when air is present in the droplet. An
example is shown in Figure 14.17. The arrows point to the air bubbles in the stain. These
are expected in blood expectorated from the lungs or from the mouth.
Figure 14.17 Expectorated blood: Air pockets in stain. Photograph by Robert C. Shaler
Introduction to Bloodstain Pattern Analysis
405
14.5 Archiving Bloodstain Patterns
The process of archiving evidence was discussed previously in Chapters 6, 7, and 8, and
those principles still apply. However, scene investigators are not BPA analysts, but they
need to understand and recognize those principles and then follow the guidelines below to
properly preserve evidence. The best way to learn how to recognize important bloodstain
patterns is to study bloodstain patterns and the underlying scientific principles relevant to
BPA, take an approved BPA workshop, gain on-scene experience, and by experimentation.
Even the student and novice scene scientist/investigator can learn to recognize patterns
that should be archived. Examples of bloodstains patterns are posted on the Internet and
are described in texts.
The BPA analyst, student, or novice scene scientist/investigator should approach each
bloodstain pattern analytically, hopefully applying the reasoning presented throughout
this text. The first step is to examine the bloodstain pattern carefully to ascertain its overall
characteristics. The next step is to try to answer the following questions:



How much area does the pattern encompass?
Is the pattern a composite of multiple patterns?
How might this pattern have occurred?
Next, the BPA analyst begins the archiving process. A useful checklist in Table 14.3
can be used as a guide.
Figure 14.18 shows a mid-range shot of a bed and the wall behind the bed taken at a
scene before scales were in place. The stains on the bed, those on the wall behind the bed,
and those on the floor next to the bed were important. Not shown in the photograph are
the cast-off stains: on the ceiling above the bed, on the wall to the left of the bed, and on the
wall opposite the bed.
Visually, there are multiple superimposed patterns that must be captured for a meaningful archive of these patterns. The photograph can be broken down into its most visually
apparent components (others are also present):


Multiple impact spatters.
Large swipe/wipe pattern on the wall behind the bed leading from just above
the bed and flowing downward toward the floor.

Smaller swipe patterns on the wall to the right of the main impact spatter.
Close-up photographs provide additional detail, for example, misting, and so on.
Capturing these patterns properly requires several photographs beginning with an establishing shot (not shown), the mid-range of each staining area (this photograph is only one
of several necessary), followed by close-ups of the relevant details present in various areas
of the overall pattern. The initial photographs are taken without scales, which should be
repeated with scales pasted on the wall. This is important to detail and preserve the overall
size of the pattern as well as subpatterns within the whole.
14.6 Bloodstain Artifacts: Selected Examples
Experienced investigators know that when they arrive at the scene it is no longer virginal.
That is, it must be considered a scene that is not as it was when the crime took place. This
Introduction to Bloodstain Pattern Analysis
405
Table 14.3 BPA Archiving Guidelines
Checklist
Determine the total area the pattern covers by examining
adjoining walls, floors, and ceiling.
Measure perimeter of each area of pattern staining. Record
measurements in appropriate log.
Reason
Ensures that subsequent archiving will not
miss important areas of the pattern
Archives entire pattern without scales
which can cover droplets from adjoining
or overlapping patterns
Bloodstain patterns should be photographed first in the raw,
without scales, so that subsequent analysis is not hindered
by their presence.
Photograph the area(s) without scales.
Cordon off each pattern using adhesive measuring tape ruled
in inches. Include the entire pattern—width and length.
Photograph the pattern with the scales in place using
forensically appropriate photos: establishing, mid-range and
close-ups, if appropriate. If not possible to capture its
entirety, grid the area and photograph each grid separately.
Video record the pattern using a digital camera having video
capability (or use a dedicated video camera). Capture each
area of the pattern. Show relationship of each to the whole.
Capture areas adjacent to the pattern (e.g., walls, floor, and
ceiling).
Photograph each area of the pattern having special
characteristics.
 Radial impact spatter might have value in determining the spatial area of the impact. If analysis is
not done at scene, capture individual droplets
(numbered sequentially and taped to the surface)
for length/width measurements for stain pattern
analysis software.
 Impact pattern with imbedded mist pattern—capture the latter, measuring overall size and that of
representative droplets.

Scales ensure that the size (width and
length) of a pattern is captured
Gridding is a least preferred method, but is
useful to capture detail in extremely large
patterns
Gives the BPA analyst the overall
perspective of the pattern
Alerts the BPA analyst with regard to
pattern complexity or to the fact that the
information within the pattern might have
additional interpretative data
Complex pattern with multiple overlapping characteristics, (multiple impact patterns and/or multiple cast-off patterns or is an impact pattern
containing cessation cast-off). Capture subpatterns separately showing relationship to overall
pattern.
is true for many reasons, some of which were discussed in Chapter 4 under the topic of
evidence dynamics (Section 4.4). Blood evidence is not exempt from the ravages of evidence dynamics. Examples of things that happen to blood evidence range from clean-up
activity to officials responding to the scene to emergency medical personnel trying to save
lives and even common weather complications. Another common concern is artifacts, Q11
which can occur from people who work on the scene to insects who dine or traipse through
the scene. The following illustrates how insect activity can affect blood stain patterns at
the scene.
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Crime Scene Forensics
Figure 14.18 Mid-range photograph of bloodstains at scene. (Photograph by Robert C. Shaler.)
14.6.1 Insect Activity
It is well known by experienced BPA analysts that insects can leave artifactual marks in
blood at the scene. Forensic entomologist Jason H. Byrd wrote [40],
Insects can also affect the interpretation of blood spatter pattern analysis. Roaches simply
walking through pooled and splattered blood will produce tracking that may not be readily
recognizable to the untrained observer. Specks of blood in unique and unusual areas (such as
on ceilings) may mislead crime scene technicians unless they are aware of the appearance of
blood contaminated roach tracks. Similarly, flies and fleas may also track through pooled and
spattered blood. However, flies will also feed on the blood and then pass the partially digested
blood in its feces, which are known as ―flyspecks.‖ Flies will also regurgitate and possibly
drop a blood droplet on a remote surface, which may serve to confuse bloodstain analysis.
Fleas feeding on the living pass a large amount of undigested blood (used as the larval food
source) on many household surfaces. If a crime occurs in a heavily infected apartment, fecal
drops already present would serve to confuse analysts as those droplets would test positive for
human blood. Therefore it is important to recognize and properly document the natural
artifacts that may occur from the presence, feeding, and defecation of roaches, flies, and fleas.
14.6.1.1 Flies
Contamination and artifacts from insects dining on dried or wet blood at the scene should be
anticipated by the BPA analyst, and scene scientists/investigators should understand that such
activity is common. Figure 14.19 shows an example of a bloodstain pattern from fly activity.
Artifactual staining could have confused BPA analysts but that from flies should not have.
The shapes and sizes of the individual stains are characteristic of the patterns that
form, and these have been described comprehensively by Suhra et al. [41]. An overview of
their results is presented in Table 14.4.
14.6.1.2 Cockroaches
Cockroaches also feast on blood at the scene. And like flies, they leave telltale marks of
their activity that can be misinterpreted by inexperienced scene scientists/investigators.
An illustration is shown in Figure 14.20.
14.6.2 On-Scene Activity
Figure 14.21a and b illustrate how crime scene unit activity can affect bloodstains. Note the
wall next to the deceased. Figure 14.21a shows the bloodstain patterns before the crime
Introduction to Bloodstain Pattern Analysis
407
Figure 14.19 Fly artifact bloodstains on wall. (Photograph by Ralph R. Ristenbatt III. Used with
Permission)
scene arrived at the scene and began working. Figure 14.21b shows the bloodstain artifacts
after the unit had completed processing the scene but before the body had been removed.
Both figures illustrate the importance of on-scene archiving before actively working on the
scene or removing evidence. The bloodstain artifacts on the wall in Figure 14.21b were created by the crime scene unit after removing the evidence from the corner—seen in Figure
14.21a. The perspective shown in each figure is slightly different, which is why some of the
detail in Figure 14.21a is missing in Figure 14.21b.
14.6.3 Fabrics: Differential Absorption
Interpreting bloodstain patterns from blood deposited on garments can pose problems
because modern fabrics are often blends of different types of fibers, each of which has different absorptive properties. This is illustrated in Figure 14.22. Note how the blood was
wicked horizontally (yellow arrow).
14.7 Becoming a BPA Analyst
The organizations associated with BPA, SWGSTAIN and the IABPA recommend specific
training courses of instruction for investigators who desire to be BPA analysts. The IAI
offers a certificate program and SWIGSTAIN has recommended quality assurance guidelines for agencies performing BPA analysts.
Table 14.4 Overview of Fly Bloodstain Characteristics
Type
Fecal
Vomit/regurgitation
Trailing (swiping due to
defecation)
Characteristics
Symmetrical and asymmetrical round spots having three levels of
pigmentation: creamy, brownish, and dark.
Craters from sucking activity are surrounded by raised edges having
a dark perimeter. The surface is irregular and reflective.
Distinguished by two segments, a body and a tail, appearing spermlike, tear–shaped, or snake-like.
Size (mm)
0.5–4
1–2
4.8–9.2
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Crime Scene Forensics
Figure 14.20 Cockroach bloodstain patterns. (Photograph Ralph Ristenbatt II. Used with permission.)
Figure 14.21 (a) Bloodstain patterns at scene. (b) Bloodstain artifacts introduced by
investigators. Photograph by Robert C. Shaler
Introduction to Bloodstain Pattern Analysis
415
Figure 14.22 Bloodstain artifact pattern in fabric. Photograph by Ralph Ristenbatt III. Used with
Permission.
14.7.1 SWGSTAIN Recommended Guidelines for Training
SWGSTAIN recommended pretraining (skills, knowledge, abilities) educational requirements for an individual currently in or entering into a BPA training program and the
minimum training requirements for trainees before practicing as a BPA analyst.
SWGSTAIN also requires a mentorship, whose responsibility it is to evaluate the trainee’s
progress toward completing the required education and training objectives stated in the
BPA analyst curriculum. Table 14.5 was adapted from the SWGSTAIN guidelines published by the IABPA in March 2008 [42].
14.7.2 BPA Certification
The IAI offers a program to certify BPA analysts. The program consists of 40 h in an
approved workshop that provides theory, study, and practice including [42]:




Flight characteristics and stain patterns.
Examination and identification of bloodstain evidence.
Documentation of blood stains and patterns.
Oral and/or visual presentation of physical activity of blood droplets
illustrating blood as fluid being acted upon by motion or force. Past research, treatise,
or other reference materials for the student.

Laboratory exercises that document bloodstains and standards by
previous research. Exercises must include—but not be limited to those listed in
Table 14.6.
Other categories of the certification program include the preparation of a laboratory
manual with a glossary of approved terms that describes the exercises performed and
observations made. Other topics of the course of instruction include knowledge of the
preservation and adequate documentation of BPA evidence.
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Crime Scene Forensics
Table 14.5 Summary of SWGSTAIN Guidelines for BPA Training
Category
Minimum training requirements
for BPA trainees
Education
Required minimum objectives
through accepted training
methods specific to BPA training
Description
Bachelor’s degree in field of study related to BPA from accredited
college or university.
Associate’s degree or equivalent in a field of study related to BPA from
accredited college or university and 2 years of job-related experience.
High school diploma or equivalent and 4 years of job-related, but not
limited to, experience as crime scene technician, criminalist,
homicide/criminal investigator.
1. Demonstrate an understanding of health and safety issues
associated with BPA.
2. Demonstrate an awareness of bloodborne pathogens and other
related health hazards.
3. Demonstrate an awareness of biohazard safety equipment and
procedures.
4. Demonstrate knowledge of the history of BPA.
5. Demonstrate an understanding of the scientific principles as they
relate to BPA.
6. Demonstrate an understanding of the scientific method and its
application to BPA experimentation, to include:
a. Problem identification
b. H yp o t h e s i s
c. Experimentation/data collection
d. Data analysis
e. Theory/conclusions
7. Demonstrate an understanding of the principles of physics as
they relate to BPA, to include:
a. Physical laws of motion
b. Surface tension
c. V i sco s it y
d. Gravity
e. Air resistance
f. V e lo cit y
8. Demonstrate an understanding of bloodstain pattern principles
and their application to BPA.
9. Demonstrate an understanding of blood components and related
human anatomy and physiology.
10. Demonstrate an understanding of the effects of target surface
characteristics on the resulting bloodstain patterns.
11. Demonstrate an understanding of the effect of
environmental factors on the formation and/or drying
time of bloodstain patterns, to include:
a. Air flow
b. Humidity
c. Te mp e r atu r e
d. Substrate characteristics
e. Animal/insect activity
12. Demonstrate an understanding of the characteristics of blood in
motion, to include:
a. Drop formation
b. O s ci ll at ion
Introduction to Bloodstain Pattern Analysis
415
Table 14.5 (continued) Summary of SWGSTAIN Guidelines for BPA Training
Category
Mentorship
Description
c. Flight paths
d. Accompanying drop
e. Wave cast-off
f. Distribution of stains
g. Kinetic energy
13. Demonstrate an understanding of health and safety issues
associated with BPA.
14. Demonstrate an awareness of bloodborne pathogens and other
related health hazards.
15. Demonstrate an understanding of the mathematical principles
that relate to BPA, to include knowledge of the methods used to
measure bloodstains and bloodstain patterns. These include:
a. Methods for the measurement of individual bloodstains.
b. Trigonometric functions as they relate to BPA.
c. Methods for origin determination.
16. Demonstrate an understanding of how the physical
appearance of bloodstain patterns (size, shape,
distribution, and location) relates to the
mechanism by which they were created.
17. Demonstrate the ability to identify bloodstain patterns.
18. Demonstrate acceptable documentation methods of bloodstain
pattern evidence, including documentation techniques specific to
BPA, to include:
a . P hoto gr aph y
b . Sketching
c . N ot e- ta kin g
19. Demonstrate an understanding of the methodologies for the
preservation and collection of bloodstain pattern evidence that
allow for future examination(s).
20. Demonstrate an understanding of bloodletting injuries, their
locations, and their potential effects on the bloodstain pattern(s).
21. Demonstrate an understanding of searching, chemical testing,
and enhancement techniques as they pertain to bloodstains.
22. Demonstrate an understanding of the limitations of BPA.
23. Demonstrate the ability to apply BPA to assist in the
reconstruction of a bloodletting event(s).
24. Demonstrate the ability to communicate findings, conclusions,
and opinions by written and/or verbal methods.
Document and participate in a mentorship program. This training
should include, but is not limited to, the evaluation of the required
objectives, the review of completed casework, supervised BPA scene
and laboratory work, and the observation of expert testimony.
Competency testing Participate in and successfully complete a competency test prior to
performing independent analysis and rendering expert opinion.
Competency testing may be administered incrementally and/or
cumulatively to allow the trainee to conduct some of the analyses
independently.
Continuing education
A minimum of 8 h of training related to BPA should be completed
annually. This may include, but is not limited to, attending
professional conferences, seminars, and/or workshops.
continued
412
Crime Scene Forensics
Table 14.5 (continued) Summary of SWGSTAIN Guidelines for BPA Training
Category
Description
Minimum requirements for BPA
mentor
Membership to a professional organization(s) related to BPA is
recommended.
1. A mentor must be an active practitioner in the field of BPA and
should have a minimum of 3 years of casework experience as a
qualified BPA analyst.
2. A mentor should have fulfilled all previously stated requirements
for a BPA analyst.
Entrance to the program includes 3 years of practice in BPA, an approved 40-h BPA
course, an approved 40-h course in photography, and 240 h of instruction in fields of study
relating to BPA, such as crime scene investigation, evidence recovery, blood detection techniques, medicolegal death investigation, and forensic science and technology. The IAI provides a reading list, and the written examination includes the following topics:









BPA terminology
Documentation, photography, illustration and sketching of bloodstains and
bloodstain patterns
Wound pathology
Investigative procedures
Crime scene processing
History of BPA
BPA theory and logic
Mathematics (basic understanding pertaining to discipline applications)
Stain and stain pattern recognition (characteristics and visual recognition)
The IAI certification program [43] seems rigorous, but it lacks the necessary scientific rigor necessary to ensure that BPA analysts completely understand the scientific
basis of how and why patterns form at crime scenes. As of this writing, the IAI specifies
no requirement that BPA analysts have a degree in science or at least college level courses
in biochemistry or physics with an emphasis in fluid dynamics, and so on, as delineated
in Section 14.3.
Table 14.6 Laboratory Exercises for BPA Certification
Category
Falling blood
Surface considerations
Blood in motion
Increased blood volumes
Flow patterns (horizontal/vertical)
Projected bloodstains and patterns
Forceful impact spatter patterns
Transfer stains and impression patterns
Other topics—not required
Introduction to Bloodstain Pattern Analysis
415
Table 14.7 Quality Assurance Guidelines for BPA
Standard
Personnel and qualifications
Description
The agency must have written specifications defining the
minimum education, training, and experience required of an
individual in order to perform BPA as per the SWGSTAIN
education and training documents.
Standard operating procedures: The agency
must have written and approved standard
operating procedures regarding BPA.
Items that should be included are:
3.1. Title
3.2. Scope
3.3. Equipment, materials, and reagents
3.4. Procedures
3.5. Report generation, review, and approval
3.6. Calculations
3.7. Limitations
3.8. Safety
3.9. References
3.10. Standard operating procedure approval
Case files
Assessments
The agency must have written procedures for the content and
maintenance of BPA case files.
The agency should have in place a documented program of
ongoing skill assessment of the bloodstain pattern analyst.
a. It is recommended that each bloodstain pattern
analyst participate in case reanalysis or
proficiency testing annually.
b. It is recommended that the agency have a documented
program that annually assesses the testimony of each
bloodstain pattern analyst.
Corrective action
The agency should establish written procedures to be followed
for corrective actions addressing such issues as
administrative, analytical, interpretive, or skill-assessment
errors.
Safety
The agency should maintain a documented health and safety
program. This should include health and safety practices
consistent with standards for the occupational exposure to
bloodborne pathogens and occupational exposure to
hazardous chemicals used in BPA.
Facilities
The agency must have a documented program that ensures
that the facility is secure from unauthorized access and
maintained in a condition that minimizes the risk of
contamination of evidence.
Evidence control
The agency must have a documented evidence control system
to ensure the integrity of physical evidence.
The agency should have a documented program to monitor
the maintenance and calibration of equipment and/or
instrumentation that affect(s) the accuracy and validity of
the BPA.
Equipment and reagents
The agency should have in place documented procedures for
testing the reagents used in casework to ensure their
functionality.
414
Crime Scene Forensics
14.8 Quality Assurance Guidelines for BPA
The recommended quality assurance program for BPA analysts resembles most reasonable
quality assurance programs in forensic science, for example, the American Society of
Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB) Legacy
Program. The purpose of a comprehensive quality assurance program is to ensure that
the users of the service provided receive a quality product. This begins with management
and goes to on-scene testing and collecting, packaging, and preserving evidence.
Table 14.7 lists these guidelines as adapted from the list described in the IABPA
March 2008 newsletter [42].
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