1. How is it a source of forensic evidence?
Origin(s) of bloodstain
Distance of bloodstain from target
Direction from which blood impacted
Speed with which blood left its source
Position of victim & assailant
Movement of victim & assailant
Number of blows/shots

2. Blood Spatter Determining Distance Blood Falls
Blood drops fall as small spheres

3. Blood Spatter Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

4. Blood Spatter Determining Distance Blood Falls
Drops form circle when hitting surface
Size depends on speed of blood drop

5. Blood Spatter Determining Distance Blood Falls
Faster drop = larger diameter (size)
Higher distance = larger diameter
Due to air resistance, speed maxes out at distances above about 7 feet

6. Blood Spatter Determining Distance Blood Falls
However, size of drop also depends on the volume of the drop.
Volume depends on object blood originated from (needle = small; bat = large)

7. Blood Spatter Effect of Surface Smooth surface = smooth sphere
Rough/porous surface may cause some splatter

8. Six Patterns Blood can be classified:
Passive Fall - Blood falling directly to floor at 90-degree angle will produce circular drops, with secondary satellites being more produced if surface hits is textured

9. Six Patterns Blood can be classified:
Arterial spurts or gushes – typically found on walls or ceilings caused by pumping action of the heart

10. Six Patterns Blood can be classified:
Splashes – shaped like exclamation points.
Shape and position of spatter pattern can help locate the position of the victim at the time of the attack

11. Six Patterns Blood can be classified:
Smears – left by bleeding victim depositing blood as he or she touches or brushes against a wall or furniture
transfers

12. Six Patterns Blood can be classified:
Trails – can be left by bleeding victim depositing blood as he or she moves from one location to another.
Can be round, smeared, appear as spurts

13. Six Patterns Blood can be classified:
Pools – form around victim who is bleeding heavily and remains in one place.
If victim is moved to another location, there may be droplets or smearing connecting the first location with a second

14. Blood Spatter Determining Direction of Blood
Narrow end of a blood drop will point in the direction of travel.

15. Examination of Directionality of Blood
Momentum – keeps blood moving in direction it was traveling
As droplet moves away from source, it elongates and may produce a thinner, tail-like appearance
Tail points in direction of blood’s movement
Satellites or secondary drops may appear in front of moving droplet of blood

16. Blood Spatter and Angle of Impact
ANGLE of IMPACT - the acute angle formed between the direction of the blood drop and the plane of the surface it strikes.

17. Angle of Impact Calculations
accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the formula below:
sin A = W / L
W – Width of blood drop
L – Length of blood drop

18. Blood Spatter Determining Direction of Blood
The angle can be determined mathematically.
Width/Length, then take the inverse sin (sin-1).
This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)

19. EXAMPLE
Finding A
LENGTH = 5.9cm
WIDTH = 2.6cm

20. SOLUTION:
A = SIN-1 W / L
A = SIN-1 2.6/5.9
A = SIN-1 (.44)
A = 26.2°

22. Blood Spatter Determining Direction of Blood
If more than one drop (from spatter) results, the point of origin can be determined

23. Blood Spatter Determining Direction of Blood
If more than one drop (from spatter) results, the point of origin can be determined

24. Blood Spatter Determining Direction of Blood
This is a 2-dimensional point of origin.
It is possible to determine the 3-D point of origin

25. Blood Spatter
For each blood drop, a string can be guided back to the point of origin.

26. Area of Origin lies at a point in space above the area of convergence.
Measurement of the impact angle allows for translation of the 2-D image (convergence) into a 3-D one (origin).

27. Area of Origin
First measure the distance from each blood stain along its central axis to the AOC (distance = y)
Then take the TAN of the degrees A.
Third, multiply the TAN of the A by the distance.
Measure that distance from the floor up the perpendicular axis and you will arrive at the Area of Origin (AO)
FORMULA: AO = TAN (A) x y

28. Finding AO EXAMPLE GIVEN:
DISTANCE FROM BLOODSTAIN (to AOC): 90cm A (calculated from A formula): 30°
SOLUTION:
= TAN (30°) x 90cm
AO = .577 x 90cm
= 52cm

30. Computer Programs Used

31. Blood Spatter Spattered Blood
In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.
Low impact = beating
High impact = gunshot

32. Blood Splatter Analysis—Six Patterns
Describe each of these based on the images above:
a. passive drops
b. arterial gushes
c. splashes
d. smears
e. trails
f. pools
Forensic Science: Fundamentals & Investigations, Chapter 8