Download Crime Scene Forensics, LLC Examining and Documenting Blood

Forensic Science 4-U
Unit: Blood Spatter Analysis
Crime Scene Forensics, LLC
Examining and Documenting Blood Stain Patterns
Bloodstain Pattern Analysis: is the examination of the shapes,
locations, and distribution of patterns of bloodstains, in order to provide
an interpretation of the physical events that gave rise to their origin.
The following Information may be obtained from a proper Bloodstain Pattern Analysis:
1. Distance from the blood source to the target
2. Direction of travel and impact angles
3. Nature of the force used to cause the bloodshed
4. The object used to cause the bloodshed
5. Sequencing of multiple bloodshed events
6.Interpretation of contact or transfer patterns
When properly documented, bloodstain patterns found at the crime scene, or on a
particular person's clothing, can be used to:
1. Confirm or refute the position of a victim, witness, suspect, or defendant
2. Determine if there is evidence of a struggle, or if the assault is "one sided"
3. Confirm or refute statements made by principles in the case:
IE: Are stain patterns on a particular person's clothing consistent
with accounts given by the victim, witness, or defendant?
Blood Flight Characteristics:
 Blood will not break up unless it is acted upon by
force. The force must be great enough to overcome the
surface tension of the blood.
 Blood forms a spherical shape (perfect circular shape)
almost immediately upon separating from the blood source.
The spherical shape is caused by the surface tension of the
blood.
 Surface Tension causes the blood drop to pull itself in;
both horizontally and vertically.
 The blood drop will settle into a spherical shape, as a
result of the surface tension.
 The surface tension will maintain the sphere shape of
the blood drop until it impacts with the surface.
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Forensic Science 4-U
Unit: Blood Spatter Analysis
SPATTER VS TRANSFER: The simplest type of blood spatter analysis is determining
spatters from transfers. Spatters are created when blood is acted upon by force, and
travels through the air before landing on a target surface. Transfers occur when a blood
source comes in direct contact with a target surface area.
TARGET SURFACE TEXTURE:
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Bloodstains can occur on a variety of surfaces. The type of surface that free falling
blood strikes affects the appearance of the resulting spatter.

Blood drops on a rough surface will make an irregular shaped stain with rough or
jagged edges.
IMPACT SPATTERS: are random patterns of spatter of varying sizes
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Forensic Science 4-U
Unit: Blood Spatter Analysis
LOW FORCE (VELOCITY) IMPACT SPATTER/PASSIVE DROPS:
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Blood that falls at the speed or force of normal gravity

These spatters usually fall from an open wound, or from a
surface that is saturated with blood
The majority of the Low Force Impact Spatters are large,
circular, spatters with diameters of 4mm or more
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Low Force Impact Spatters will increase in size as the
distance fallen increases, however, the size of the spatters
will remain constant after approximately 4 feet
MEDIUM FORCE (VELOCITY) IMPACT SPATTER:
OR PROJECTED SPATTER
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Produced with more energy or force than gravity
The force of the impact causes the blood to break into
smaller size spatters relative to the amount of force applied
This type of spatter is usually seen in blunt force, stabbings,
and secondary spatters
Produced when the majority of larger drops of blood are
broken into smaller spatters with diameters of 2 – 4 mm
The force associated with this type of spatter is greater than
25 ft. per second
HIGH FORCE (VELOCITY) IMPACT SPATTER: It is important to note that the term
"Velocity" does not measure the speed at which the blood is traveling, but rather is used
to describe or measure amount of force applied to the blood,
to cause it to spatter.
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Impact spatter that measures less than 2mm in
diameter
The force necessary to produce this size spatter
is greater than 100 ft. per second
This type of spatter is usually associated with
gunshots, explosions, and high speed collisions
High Force Impact Spatter takes on a "mist like"
appearance
If the bullet exits its target, a larger amount of high
force impact spatter may
be directed in the same direction as the bullet. This is
known as "forward spatter".
The closer to the target that the gun is fired...the great
the spatter.
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Forensic Science 4-U
Unit: Blood Spatter Analysis
DIRECTION: The "tail" points in the direction the blood drop is traveling.
ANGLE OF IMPACT: The steeper the impact, the more elliptical or elongated, the blood
drop
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Measure the width and the length of the stain/spatter sine= width = 9mm
length = 18mm
9 divided by 18 = 0.500
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Arcsine 0.500 = 30 degree angle of impact
Do not measure the “tail”, it is a secondary force or event.

Divide the smaller number by the larger number
Reference:
Crime Scene Forensics, LLC. (n.d.). Interpreting Bloodstain Patterns. Retrieved October 17, 2011, from
Crime Scene Forensics: http://www.crimescene-forensics.com/Blood_Stains.html
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