1. BLOOD SPATTER ANALYSIS
Jennifer Pechal

2. Blood stain pattern analysis
“When liquid blood is acted upon by physical forces, bloodstains and bloodstain patterns may be deposited on various…patterns can yield valuable information concerning the events which lead to their creation when examined by a qualified analyst.  ” (IABPA)
“The examination of the shapes, location, and distribution patterns of blood stains, in order to provide an interpretation of the physical events which gave rise to their origin.” (J. Slemko Forensic Consulting)

3. Why is it important in forensics?
Confirm or refute assumptions concerning events and their sequences
Suspect’ s account
Victim’s account
Bloodstain evidence may reveal:
Area(s) of origin
Number of blows or shots
Type and direction of impact that produced bloodshed
Movement and direction of a person or object
Movement of victim after bloodshed
Potentially the assailant
Reconstruct events

4. History
1895 – Dr. Eduard Piotrowski published first reference to bloodstain pattern analysis
1939 – Dr. Victor Balthazard the first to use physical interpretation of stains
1955 – Dr. Paul Kirk used blood stain evidence in State of Ohio v Samuel Sheppard
1973 – Dr. Herbert MacDonell conducted first training program for blood spatter in Jackson, MS

5. Blood Makes up approximately 8% of the weight in a human body
Males have approximately 5 – 6 L
Females have approximately 4 – 5 L
Blood comprised of two parts:
Hematocrit
Red blood cells
White blood cells
Platelets
Plasma
Gases
Ions
Nutrients molecules
Proteins, fats, hormones

6. Properties of blood Some blood properties can be compared to water:
Blood is 6x more viscous than water
Gravity of blood is slightly higher
Blood droplets stay round because of surface tension
Water
Blood
Viscosity
1.0 mP·s-1
3-4 mP·s-1
Surface tension
0.073 N·m-1
0.058N·m-1
Density
1000 kg/m3
1060 kg/m3

7. Surface Tension
Surface tension is an upwards force that allows the surface of a liquid to act as an elastic sheet
Free falling blood will stay intact until acted upon by an exterior force
When it strikes another object
When acted upon by another force

8. Phases of impact 1. Contact/Collapse Droplet hits the object
Collapses from the bottom up

9. Phases of impact 2. Displacement
Slight dimples and spines begin to form based on the irregularities on the impact surface
Top view
Side view

10. Phases of impact 3. Dispersion
Most of the volume of the blood is forced to the rim
Create satellite spatter
Top view
Side view

11. Phases of impact 4. Retraction
Surface tension trying to keep the droplet together
Satellite spatters that have enough momentum can form completely separate stains
The droplet can “burst” if the force pulling it apart is great enough
Side view
Top view

12. Size and Shape
A blood droplet released from a shorter height will be smaller than a blood droplet released from a higher height
Spatter size is dependent upon velocity
Low velocity spatter = 5 ft/sec
Medium velocity spatter = 5 – 25 ft/sec
High velocity spatter = 100+ ft/sec

13. Low velocity spatter 3 mm or greater in diameter
Blood falls under the influence of gravity
Blood trail motion can prove directionality
Result from weapon cast-off, a person remaining still, walking, or running

14. Medium velocity spatter
1 – 3 mm in diameter
Indicates blunt force trauma, sharp trauma, or cast- off

15. High velocity spatter Smaller than 1 mm in diameter
Appears as a fine spray or misting
Resulting from gunshot trauma, power tools, an object striking with extreme velocity, or an explosion

16. Directionality
width = 1.0, length =1.0, which corresponds to an impact angle of 90 degree
width = 1.0, length = 2.0, which corresponds to an impact angle of 30 degrees
sin i = (width/length)
arcsin i = angle of impact

17. What direction did the blood originate?

18. Area of convergence Determine directionality of the blood droplets
Lines must be drawn away from the direction of travel towards the origin
Draw straight lines using the “oval” of the blood droplet
Lines should run along the length
The direction of the blood droplet
Measure from the back of the stain
Area of convergence

19. Area of origin Identify the AOC this will be the z- axis
Calculate the angle of impact for each blood droplet
Attach a string for each droplet at it’s specific angle to the z-axis
Repeat for each droplet

20. Types of blood spatter
Arterial

21. Types of blood spatter
Transfer

22. What caused this pattern?

23. A gun impression

24. What caused this pattern?
Hair

25. What caused this pattern?
Flies

26. What caused this pattern?
Maggots

27. Questions?