Bloodstain Pattern Analysis
CHAPTER 10
Introduction to Blood
Did you know
 You can loose up to 40% of your blood
volume and still survive.
 Beyond that and death is certain.
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


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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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Passive
 Passive Bloodstains
 Patterns
created from the force of gravity
 Drop, series of drops, flow patterns, blood pools, etc.
Determining Distance Blood Falls
Drops form circle when hitting surface
 Size depends on speed of blood drop

Blood Spatter
Determining Distance Blood Falls
Faster drop = larger diameter (size)
 Higher distance = larger diameter


Due to air resistance, speed maxes out at
distances above about 7 feet
Blood Spatter
Determining Distance Blood Falls

However, size of drop also depends on the
volume of the drop.

Volume depends on object blood originated
from (needle = small; bat = large)
Blood Spatter
Since the volume of blood in a drop is
unknown…
The distance a drop has fallen
cannot be measured.
Effect of Surface
Smooth surface = smooth sphere
 Rough/porous surface may cause some
splatter

Transfer or Contact
 The pattern created when a wet, bloody object comes in
contact with a target surface; may be used to identify an
object or body part.
Projected bloodstains
–
–
–
Patterns that occur when a force is applied to the
source of the blood
Low, medium, or high impact spatters, cast-off, arterial
spurting, expiratory blood blown out of the nose, mouth,
or wound.
Narrow end of a blood drop will point in the direction of
travel.
Images from http://www.bloodspatter.com/BPATutorial.htm
Determining Direction
 By utilizing trigonometric functions its
possible to determine the impact angle for
any given blood droplet.
 SIN 0 = width (a)

length (c)
SIN < = Width (a) 1.5cm
Length (c) 3.0cm
Width (a) 1.5cm = SIN <
Length (c) 3.0cm
0.5 = SIN <
< = 30 degrees
Impact
 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.
 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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Blood Spatter
Determining Direction of Blood

If more than one drop (from spatter) results,
the point of origin can be determined
Blood Spatter
Determining Direction of Blood

If more than one drop (from spatter) results,
the point of origin can be determined
Blood Spatter
For each blood
drop, a string
can be guided
back to the point
of origin.
Blood Evidence
 Class evidence for blood would include blood type.
If you can determine the DNA you would have
individual evidence.
 Blood stain patterns are considered circumstantial
evidence in a court room. Experts could argue
many points including direction of travel, height of
the perpetrator, position of the victim, left/right
hand, whether the body was moved, etc.
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http://www.nfstc.org/links/animation
s/images/blood%20spatters.swf