BLOODSTAINS
PATTERN ANALYSIS
Questions Answered by
Blood Spatter Interpretation
 The distance between the target surface and the origin of blood
 The point(s) of origin of the blood
 Movement and direction of a person or an object
 The number of blows, shots, etc. causing the bloodshed and/or
the dispersal of blood.
 Type and direction of impact that produced the bloodshed
 The position of the victim and/or object during bloodshed
 Movement of the victim and/or object after bloodshed
Summary
 Establish the relationship between dropping
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height and blood drop diameter
Differentiate between high velocity and medium
velocity impact spatter
Recognize patterns around the drop, such as
satellite spatter or spines
Create and examine vertical blood drop patterns
on various textured surfaces
Identify a point of convergence and point of
origin
Blood Droplet Characteristics
 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.
 A droplet falling from the same height,
hitting the same surface at the same angle,
will produce a stain with the same basic
shape.
 How will the shape change as the height is
increased or decreased?
Types of Bloodstain Patterns
 Passive Bloodstains
 Patterns created from the force of gravity
 Drop, series of drops, flow patterns, blood pools, etc.
• Projected Bloodstains
– Patterns that occur when a force is applied to the
source of the blood
– Includes low, medium, or high impact spatters, castoff, arterial spurting, expiratory blood blown out of
the nose, mouth, or wound.
• Transfer or Contact Bloodstains
– These patterns are created when a wet, bloody object
comes in contact with a target surface; may be used to
identify an object or body part.
– A wipe pattern is created from an object moving
through a bloodstain, while a swipe pattern is created
from an object leaving a bloodstain.
Images from http://www.bloodspatter.com/BPATutorial.htm
Conditions Affecting
Shape of Blood Droplet
 Size of the droplet
 Angle of impact
 Velocity at which the blood droplet left its origin
 Height
 Texture of the target surface
 On clean glass or plastic—droplet will have smooth outside
edges
 On a rough surface—will produce scalloping on the edges
Blood Spatter (or splatter)
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and
sizes to reconstruct the crime scene.
Blood Spatter > Distance
Determining Distance Blood Falls
Blood drops fall as small spheres
Blood Spatter > Distance
Determining Distance Blood Falls
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Drops form circle when hitting surface
Size depends on speed of blood drop
Blood Spatter > Distance
Determining Distance Blood Falls
Faster drop = smaller diameter (size)
Higher distance = larger diameter
Due to air resistance, speed maxes out at
distances above about 7 feet
Blood Spatter > Distance
Determining Distance Blood Falls
However, size of drop also depends on the
volume of the drop.
Volume depends on the object blood
originated from (needle = small; bat = large).
Blood Spatter > Distance
Determining Distance Blood Falls
Since the volume of blood is unknown…
The distance a drop has fallen
cannot be measured.
Blood Spatter/ Velocity
Types of Spatter
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Spattered Blood = random distribution of
bloodstains that vary in size
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Amount of blood and amount of force affect
the size of blood spatter.
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Can result from gunshot, stabbing, beating
Blood Spatter/ Velocity
Spattered Blood can:
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Help determine the location of the origin of
the blood source.
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Help determine the mechanism which
created the pattern.
Blood Spatter/ Velocity
Spattered Blood
In general, for higher impacts, the pattern is
more spread out and the individual stains
are smaller.
Low impact = beating
High impact = gunshot
Impact spatter
 Results from the application of energy to a
source of wet blood
 Arises from kicking, punching, or firearms
 Mist – very fine spatter (.01 mm)
 Usually a product of a gunshot
 Fine – mainly 2mm or less
 Suggestive of beating type assault
 Medium – 2mm – 6mm in diameter
 Suggestive of weapon cast off
 Large - >6mm
 Suggestive of dripping blood
 Note that sneezing or coughing could cause
similar patterns as above
Low Velocity Spatter
 Gravitational pull up to 5 feet/sec.
 Relatively large stains 4mm in size and
greater
Medium Velocity
 Force of 5 to 25 feet/sec.
 Preponderant stain size 1
to 4mm in size
 Beating and Stabbing
Spatter = larger individual
stains
 First blow usually
doesn’t result in spatter
since there is not yet any
exposed blood
High Velocity
 Force of 100 feet/sec. and greater
Preponderant stain size 1mm in size and
smaller
Mist like appearance
 Gunshot Spatter = can result in a mist-like
spatter that indicates a gunshot.
Blood Spatter/ Velocity
Types of Spatter
Gunshot Spatter = can result in a mist-like
spatter that indicates a gunshot.
 Not all gunshots will result in misting.
 If misting is present, it is most likely a
gunshot.
Gunshots result in back spatter (where
bullet enters) and forward spatter
(where bullet exits).
Blood Spatter
Types of Spatter
Satellite Spatter = free falling drops of blood
that fall onto a spatter pattern.
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These drips are usually much larger than
impact spatter.
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However, blood dripping into blood can
create a spatter.
Blood Spatter
Effect of Surface
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Smooth surface = smooth sphere
Rough surface may cause some splatter
Blood Spatter > Direction
Determining Direction of Blood
Narrow end of a blood drop will point in the
direction of travel.
Blood Spatter > Direction
Determining Direction of Blood
If more than one drop (from spatter) results,
the point of origin can be determined
Blood Spatter > Direction
Determining Direction of Blood
If more than one drop (from spatter) results,
the point of origin can be determined
Blood Spatter > Direction
Determining Direction of Blood
This is a 2-dimensional point of origin called point of
convergence
It is possible to determine the 3-D point of origin
Blood Spatter > Direction
Determining Direction of Blood
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The angle can be determined
mathematically.
Width/Length, then take the
inverse sin (sin-1).
This number is the impact
angle (90 = perpendicular to
surface; <10 at a sharp angle)
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; the angle can be
determined by the following formula:
Blood Spatter > Direction
For each blood
drop, a string can
be guided back to
the point of origin.
Blood Spatter/Other Types
Other Types of Spatter
Castoff Pattern = Blood flung off of
swinging object.
Can reconstruct where assailant and victim
were positioned.
Blood Spatter/Other Types
Other Types of Spatter
Expirated Bloodstain Pattern = Blood can
accumulate in lungs, sinuses, and airway.
Forcibly exhaled.
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Can appear like beating or gunshot pattern.
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May be mixed with saliva or nasal
secretions.
Arterial Blood
 Patterns are caused by the
pressure within the arterial
system
 Will depend on:
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Damage to the artery
Site of the injury
Presence of clothing
Direction of spurting
Distance of target surface
 Patterns are usually the
same size
Contact
 Contact smears usually
arise from contact of a
bloodstained item with
a non-bloodstained
surface
 Can leave imprint
evidence
Blood Spatter
Alteration of bloodstain over time
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Blood dries and clots over time.
Difficult to estimate the time the blood exited
the body.
Clotted smears can indicate time of movement.