Transcript Blood Spatter

BLOOD SPATTER
BLOOD SPATTER
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
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BLOOD SPATTER ANALYSIS
Analysis of a spatter pattern can aid in determining the:
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direction blood traveled
angle of impact
point of origin of the blood
velocity of the blood
manner of death
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BLOOD SPATTER ANALYSIS
Natural cohesiveness of blood
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HOW SURFACE TEXTURE AFFECTS SPATTER
BLOOD SPATTER ANALYSIS
Satellite droplets—
 When blood falls from a height, or at a high velocity,
 It overcomes its natural cohesiveness, and
 Separates from the main droplet
Spiking patterns—
 Form around the droplet
edges when blood falls
onto a less-than-smooth
surface
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BLOOD SPATTER 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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CALCULATING ANGLE OF IMPACT
Mathematically, the angle of impact can be calculated by the
equation and determining the inverse of Sine A:
Width of blood stain
Sin A =
----------------------------Length of blood stain
CLASSIFYING IMPACT SPATTER
The droplet size can be used to determine the speed in which the impact occurred
 Provides insight to crime but not specific events
IMPACT VELOCITY VS. SIZE OF DROPLET
 Low Velocity Spatter:
 Drops with diameters of 4 mm or more normally produced by an applied force of up to 5 ft/sec.
 Medium Velocity Spatter:
 Drops with diameters from 1-4 mm with an applied force of 5 to 25 ft/sec
 High Velocity Spatter:
 Drops with diameters of less than 1 mm from an applied force of 100 ft/sec or faster.
BLOOD SPATTER ANALYSIS
—SIX PATTERNS
Describe each of these:
a)
b)
c)
d)
e)
f)
Passive drops
Arterial gushes
Splashes
Smears
Trails
Pools
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IMPACT SPATTER
BLOOD SPATTER ANALYSIS
—IMPACT
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?
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CAST-OFF SPATTER
ARTERIAL SPURT SPATTER
EXPIRATED BLOOD PATTERNS
An expirated blood pattern is created by blood that is expelled
from the mouth or nose from an internal injury.
The presence of bubbles of oxygen in the drying drops or a lighter
color as a result of dilution by saliva can differentiate a pattern
created by expirated blood.
The presence of expirated blood gives an important clue as to the
injuries suffered and the events that took place at a crime scene.
BLOOD SPATTER ANALYSIS
Lines of convergence—two or blood spatters can
pinpoint the location of the blood source
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GUNSHOT SPATTER
Gunshot spatter is fine forward spatter from an exit wound and
back spatter from an entrance wound. However, the gunshot
produces only back spatter if the bullet does not exit the body.
VOID PATTERNS
A void is created when an object blocks the deposition of blood
spatter onto a target surface or object and the spatter is deposited
onto the object or person instead.
TRANSFER PATTERNS
A contact or transfer pattern is created when an object with blood
on it touches one that does not have blood on it.
SKELETONIZATION
The phenomenon of skeletonization occurs when the edges of a
stain dry to the surface.
This usually occurs within 50 seconds of deposition of droplets, and
longer for larger volumes of blood.
DOCUMENTING
Investigators should note, study, and photograph each pattern and
drop to accurately record the location of specific patterns and to
distinguish the stains from which laboratory samples were taken.
When photographing be sure to include a scale.
TECHNIQUES OF DOCUMENTATION
Two techniques used to document bloodstain patterns are:
 Grid method
 A grid of squares of known dimensions are set up over the entire pattern.
 Perimeter ruler method
 A rectangular border of rulers is set up around each pattern and a smaller ruler next to each stain.
CRIME SCENE INVESTIGATION
OF BLOOD
1.
2.
Search for blood evidence
Determine
Is the evidence blood?
b. Is the blood human?
c. What is the blood type?
a.
3.
Interpret the findings:
Does the blood type match a suspect’s blood?
b. If not, exclude that suspect
c. If yes, decide if DNA profiling is necessary
a.
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