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Unit #5 - Lecture #3

This lecture covers the basics of bloodstain pattern analysis.

Rachel Stagner

on 8 March 2016

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Transcript of Unit #5 - Lecture #3

Unit #5 - Lecture #3
Blood & Blood Spatter

Ms. Stagner

After Viewing this Lecture You Will....
Understand the physical properties of blood that allow us to perform bloodstain pattern analysis.
Understand how trigonometric relationship are used to "string" bloodstains
Review the three spatter pattern categories.
Review the different blood spatter patterns and be able to recognize them.
Reconstruction: bloodstains tell the story
Can point to more evidence
Combines with other evidence in court
Bloodstain Pattern Analysis
©Kathy Mirakovits, FSEC
Physical Properties of Blood
©Kathy Mirakovits, FSEC
Blood has a fairly high surface tension
Blood is very viscous
Blood tends to adhere to external surface
Blood that falls from body moves as an oscillating sphere
Size of spherical blood droplet depends upon size of surface from which it falls (larger surface=more volume=larger droplet)
Height of fall changes diameter of blood drop (closer to ground=smaller diameter)
Blood reaches terminal velocity at approximately 7 feet and diameter will not increase
Physical Properties of Blood
©Kathy Mirakovits, FSEC
Short Distance
Longer Distance
Impact due to blunt force
Medium Velocity Impact Spatter
- result of bloodied object receiving a blow
Must have blood on surface to create this type of pattern
First blow does not generally produce impact stain, with exception of gunshots
Bloodstains are typically 1-4 mm in size
Spatter Bloodstains
©Kathy Mirakovits, FSEC
Satellite Spatter
—protrusions from the parent blood drop
Satellite spatter
—smaller droplets that leave parent drop and land near it
Disruption of surface tension and cohesive properties of blood due to type of target surface
Physical Properties of Blood
Passive stains
move only under influence of gravity
Spatter stains
arise from a force in addition to gravity
Contact or Transfer Stains
are physically or physiologically changed
Bloodstain Pattern Categories
©Kathy Mirakovits, FSEC
Natural movement of large blood deposit
Large amount of blood hits target at one time
Large volume
Vertical drips
Passive Bloodstains
Impact Due to Gunshot
Simulating a Cast Off Pattern
High Velocity Impact Spatter
Bloodstains <1mm in length
Misty appearance

Cast Off
Linear pattern of blood leaving weapon such as knife, bat, or hand
Spatter Bloodstains
©Kathy Mirakovits, FSEC
Arterial Spurting
Large amount of blood under pressure
Arc pattern
Due to breach of major artery (carotid, femoral, etc)
Blood ejected with force from respiratory system
Similar pattern to impact spatter, but may contain air bubbles
Spatter Bloodstains
©Kathy Mirakovits, FSEC
Hand, hair, shoe, etc
—absence of blood where it should be
—existing bloodstain altered by secondary motion through it
--Bloodied object leaves transfer of blood showing motion
Contact or Transfer Bloodstains
©Kathy Mirakovits, FSEC
Important Vocabulary for Stringing Stains
Angle of Impact
: the angle at which a drop of blood hits a surface.
Area of Convergence (AOC)
: The area where lines drawn through the center of bloodstains intersect.
Point of Convergence (POC)
: One point in the center of the area of convergence that will be used to measure distance (D).
Distance (D)
: the measured length between the leading edge of the blood drop and the point of convergence
Point of Origin (P)
: The distance away from the wall that the blood stain came from. Sometimes also called "H" for height.
Full transcript