Chapter 8 Blood and Blood Splatter
By the end of this chapter you will be able to:
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Explain the composition of blood
Describe the function of blood cells
Determine the blood type of a blood sample
Conduct a blood splatter analysis
Examine wounds and describe the nature of the
weapon
Find and process blood evidence
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
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Forensic Science: Fundamentals & Investigations, Chapter 8
Introduction and History
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Blood typing provides class evidence
DNA profiling provides individual evidence
A blood splatter pattern provides information
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the truthfulness of an account by a witness or a
suspect
the origin of the blood
the angle and velocity of impact
the type of weapon used
Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
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Plasma—a liquid suspending other blood
components
Red blood cells (Erthrocytes)—carries oxygen to
the body’s cells and carbon dioxide away
White blood cells (Leukocytes)—fights disease
and foreign invaders and, alone, contain cell nuclei
Platelets—aids in blood clotting and the repair of
damaged blood vessels
Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Types of Blood Cells
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Forensic Science: Fundamentals & Investigations, Chapter 8
Cellular Components of Blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Proteins
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Discovered in 1900 by Karl Landsteiner
Identifies the presence or absence of particular
proteins embedded in the cell
Quicker and less expensive than DNA profiling
Produces class evidence but can still link a
suspect to a crime scene or exclude a suspect
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Proteins
42%
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12%
3%
of the population in the United States
Forensic Science: Fundamentals & Investigations, Chapter 8
43%
Blood Groups
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Antibody Can Give
Can Get
Blood From
Type
Antigen
A
A
B
A, AB
O, A
B
B
A
B, AB
O,B
AB
A and B
Neither
A nor B
AB
A, B, O, AB
O
Neither
A nor B
A and B
A, B, O, AB
O
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Blood To
Rh Factor
85% of the population has a protein called
RH factor on their blood cells
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Antibodies
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Antibodies are Y-shaped
proteins secreted by white
blood cells that attach to
antigens to destroy them
Antigens are foreign
molecules or cells that
react to antibodies
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Enzymes
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Enzymes are complex proteins that catalyze
different biochemical reactions
Many enzymes and proteins have been found in
the blood that are important for identification
purposes
Forensic Science: Fundamentals & Investigations, Chapter 8
Unknown Stain at a Scene
Questions to be answered:
o Is it blood?
o Is it human blood?
o Whose is it?
• Determine blood type, alcohol
content, drugs present
• Determine the method(s) in
which blood may have been
deposited
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Presumptive Tests for
Blood Determination
Kastle-Meyer color test
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A mixture of phenolphthalein and hydrogen
peroxide
The hemoglobin will cause the formation of a deep
pink color if blood is present
Not specific for blood—can turn pink in presence of
some veggies such as potatoes or horseradish
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Hematest® tablet
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Reacts with the heme group in blood causing
a blue-green color
Originally designed as a urine dipstick test
for blood
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Luminol test
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Reaction with blood to produce light
(luminescence)
Can be sprayed onto large areas
Very sensitive—can detect blood diluted up
to 300,000 times (trace patterns)
Does not degrade DNA
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Human vs Animal Blood
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Microscopic observation
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Animal Blood
Larger nucleic red
blood cells
Frog Blood
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Human Blood
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Red blood cells are most
numerous; 5 to 6 million
per mm3
White blood cells are
larger and less numerous;
5 to 10,000 per mm3
Platelets are tiny, cellular
fragments; 350 to 500,000
per mm3
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Blood Spatter
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1939—spatter patterns first
analyzed
Blood may spatter when a wound is inflicted
Blood spatter pattern—a grouping of blood
stains
Patterns help to reconstruct the events
surrounding a shooting, stabbing, or beating
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis
Analysis of a spatter pattern can aid in
determining the:
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direction blood traveled
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angle of impact
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point of origin of the blood
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velocity of the blood
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manner of death
Forensic Science: Fundamentals & Investigations, Chapter 8
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Blood Pattern Reconstruction
Scene Pattern
Reconstruction
1. Stain condition
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3.
4.
5.
Pattern
Distribution
Location
Directionality
Lab Results
Reconstruction
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2.
3.
4.
5.
Genetic marker typing
Age Determination
Source Determination
Race Determination
Sex Determination
—From “Cracking Cases” by Dr. Henry C. Lee
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Blood Droplet Characteristics
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A blood droplet will remain spherical in
space until it collides with a surface
Once a blood droplet impacts a surface,
a bloodstain is formed.
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Characteristics cont.
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A droplet falling from the same height, hitting
the same surface at the same angle, will
produce a stain with the same basic shape.
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Conditions Affecting
Shape of Blood Droplet
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Size of the droplet
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Angle of impact
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Velocity at which the blood droplet left its
origin
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Conditions cont.
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Height
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Texture of the target surface
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On clean glass or plastic—droplet will have
smooth outside edges
On a rough surface—will produce scalloping on
the edges
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Bloodstain Terminology
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Angle of impact—angle at which blood
strikes a target surface.
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Bloodstain transfer—when a bloody
object comes into contact with a surface
and leaves a patterned blood image on the
surface
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Bloodstain Terminology
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Backspatter—blood that is directed back
toward the source of energy
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Cast-off—blood that is thrown from an object
in motion
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Bloodstain Terminology
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Contact stain—bloodstains caused by contact
between a wet blood-bearing surface and a second
surface which may or may not have blood on it
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Transfer—an image is recognizable and may be
identifiable with a particular object
Swipe—wet blood is transferred to a surface which
did not have blood on it
Wipe—a non-blood bearing object moves through a
wet bloodstain, altering the appearance of the
original stain
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Bloodstain Terminology
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Directionality—relates to the direction a drop
of blood traveled in space from its point of
origin
Terminal velocity—the greatest speed to
which a free falling drop of blood can
accelerate in air.
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Dependent upon the acceleration of gravity and
the friction of the air against the blood—
approximately 25.1 feet/second.
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High Velocity
Blood Spatter
Greater than 25 feet
per second, usually
100 feet per second
Gives a fine mist
appearance
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Medium
Velocity
Blood Spatter
5 to 25 feet per
second
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Low Velocity
Blood Spatter
5 feet per second or
less
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Bloodstain Patterns
The shape of a blood drop:
• Round—if it falls straight down at a 90 degree
angle.
• Elliptical—blood droplets elongate as the angle
decreases from 90 to 0 degrees
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Natural cohesiveness of blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Impact
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The more acute the
angle of impact, the
more elongated the
stain.
90 degree angles are
perfectly round drops
with 80 degree angles
taking on a more
elliptical shape.
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At about 30 degrees
the stain will begin
to produce a tail.
The more acute the
angle, the easier it is
to determine the
direction of travel.
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Bloodstain Patterns
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The harder and less porous
the surface, the less the
blood drop will break apart.
The softer and more porous
the surface, the more a blood
drop will break apart.
The pointed end of the blood
stain faces the direction of
travel.
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Blood Splatter Analysis
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Satellite droplets—
• When blood falls from a height, or at a high velocity,
• It overcomes its natural cohesiveness, and
• Separates from the main droplet
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Spiking patterns—
• Form around the droplet
edges when blood falls
onto a less-than-smooth
surface
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
—Directionality
The shape of an individual drop of blood
provides clues to the direction from
where the blood originated.
How will the point of impact compare
with the rest of a blood pattern?
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis
Lines of convergence—two or blood spatters can
pinpoint the location of the blood source
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
—Six Patterns
Describe each of these:
a)
b)
c)
d)
e)
f)
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Passive drops
Arterial gushes
Splashes
Smears
Trails
Pools
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
—Impact
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Patterns can help investigators determine
the type of weapon used
What kind of a pattern is produced by a gun
shot?
What kind of a pattern is produced by a
hammer blow?
Forensic Science: Fundamentals & Investigations, Chapter 8
. . . . . . . . . . . . . . . . . Summary
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Blood consists of cellular components and plasma.
The various human blood types are caused by the
presence or absence of A and/or B proteins on the
surface of red blood cells.
Blood splatter evidence can be used to recreate a
crime scene.
Investigators endeavor to (a) locate, (b) identify,
and (c) interpret blood splatter patterns at crime
scenes.
Forensic Science: Fundamentals & Investigations, Chapter 8