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.
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.
Transfer - Swipe Pattern
Transfer - Wipe Pattern
Spatter Pattern
TARGET SURFACE TEXTURE:
•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 smooth surface will make a more uniform
or regular circular shape.
•Blood drops on a rough surface will make an irregular
shaped stain with rough or jagged edges.
LOW FORCE (VELOCITY) IMPACT SPATTER/PASSIVE DROPS:
•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
•Low Force Impact Spatters will increase in size as the
distance fallen increases, however, the size of the spatters
will remain constant after approx 4 feet
MEDIUM FORCE (VELOCITY) IMPACT SPATTER:
•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:
•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
IMPACT SPATTERS: are a random pattern of spatter of varying sizes
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.
Angle of Impact:
The steeper the impact, the more
elliptical or elongated, the blood drop
Direction:
The "tail" points to the direction of
the blood drop
Angle of Impact
•Measure the width and the length of the stain/spatter
sine= width = 9mm
length = 18mm
•9 divided by 18 = 0.500
•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
BACK SPATTER OR "BLOWBACK"
•When a bullet strikes a target, some high force impact spatter may be directed back toward the gun that fired the shot. This is known as "back spatter"
•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 amount of high force impact spatter created will depend upon the size or caliber of the bullet fired, as well as the distance from the gun to the target. The larger the bullet, or projectile, the greater
the spatter. The closer to the target that the gun is fired...the great the spatter.
For a complete list of bloodstain pattern terms, as recommended by the Internation Association of Blood Stain Pattern Analysts. (IABPA), go to: http://www.iabpa.org/ These terms should serve as a guide, for those who work and teach in the field of Blood Stain Pattern Analysis. These terms are not meant to be all encompassing
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