1. How is Blood Evidence used in Forensics?

2. How blood evidence is collected
Photograph!
Blood pool –collect with gauze pad or clear cotton. Let air dry and refrigerate of freeze within 48 hours.
Dried blood –wrap object in clean paper and place in paper bag.
Swab

3. Bloodstain Patterns Physical Evidence
Usually Found at Violent Crime Scenes
Gives Clues as to WHAT Happened
May Suggest Sequence of Events
Analysis MUST be placed in context of all aspects of crime scene investigation in order to reconstruct (possible) criminal events.

4. Forensic Analysis of Blood
1. Visual examination of evidence
2. Presumptive screening test (Is it blood?)
3. Confirmation test (Seriously, is it blood?)
4. Determine species origin (human blood?)
Forensic Analysis of Blood
Visual examination of evidence
Presumptive screening test (Is it blood?)
Confirmation test (Seriously, is it blood?)
Determine species origin (human blood?)
Identify the blood (whose blood is it?)
5. Identify the blood (whose blood is it?)

5. Presumptive Screening Tests
Negative result means the questioned stain is not likely blood
Positive result means the questioned stain is likely blood
Presumptive Screening Tests
Negative result means the questioned stain is not likely blood
Positive result means the questioned stain is likely blood

6. Presumptive Screening Tests
Kastle-meyer - Phenolphthalein
Color test - Positive result = pink
Used on dried blood
Phenolphthalein
Positive result = pink
False Positive – A positive result given by a substance that is not blood.

7. Presumptive Screening Tests
Luminol
Luminol is combined with oxidant and sprayed over area thought to contain blood
Emits a blue-white to yellow green glow
More sensitive than color tests
May damage blood stain (no blood/DNA typing)
Used to locate and define areas of blood
old blood stains
cleaned floor
Luminol
Emits a blue-white to yellow green glow

8. Presumptive Screening Tests
Luminol

9. Confirmatory Tests
Teichmann Test and Takayama Test
Due to the possibility of false positives with the presumptive tests, confirmatory tests are necessary
Confirmatory tests involve making crystals that detect the presence of hemoglobin
Requires a microscope
Confirmatory Tests
Due to the possibility of false positives with the presumptive tests, confirmatory tests are necessary
Confirmatory tests involve making crystals that detect the presence of hemoglobin

10. Genetic Markers in Blood
If a stain is blood, and it is human blood, then whose is it? Precipitin determines if it is animal or human blood
Blood Group Markers
If a stain is blood, and it is human blood, then whose is it?
Blood Group Markers
Protein/Enzyme Markers
DNA
Protein/Enzyme Markers
DNA (sometimes)

11. Introduction to Blood RBC = no DNA; WBC = yes DNA
All blood cells have blood groups (antigens) on outside of cell.
Introduction to Blood
RBC = no DNA; WBC = yes DNA
All blood cells have blood groups on outside of cell.
ABO Markers

12. Blood Group Markers ABO Markers (antigen and antibodies) A B AB O
Blood Type
Antigen
(blood group)
Antibody
% population A B AB O
ABO Markers (antigen and antibodies)

13. Blood Group Markers ABO Markers (antigen and antibodies) A Anti-B 40 B
Blood Type
Antigen
(blood group)
Antibody
% population A
Anti-B 40 B
Anti-A 10 AB
A & B
none 5 O H
Anti-A & Anti-B 45

14. Blood Group Markers A cells clump with anti-A
ABO Markers
A cells clump with anti-A
B cells clump with anti-B
AB cells clump with both
O cells do not clump
Rh clumping = +
A cells clump with anti-A
B cells clump with anti-B
AB cells clump with both
O cells do not clump

15. Evidence may reveal: Speed with which blood left its source
Distance of bloodstain from target
Direction from which blood impacted
Origin(s) of bloodstain
Position of victim & assailant
Weapon/Number of blows/shots
Movement of victim & assailant

16. Splash 1
5 ml blood squirted from a syringe from a height of 1 m

17. Wipe Patterns Object moves through a wet bloodstain
Feathered edge suggests direction

19. Transfer Patterns Wet, bloodied object contacts a secondary surface
Transfer from:
hand, fingers
shoes, weapon
hair
Transfer to:
walls, ceilings
clothing, bedding
Produces mirror-image of bloodied object

20. Transfer from hair 70

21. Flow Patterns Blood flows horizontally & vertically
Altered by contours, obstacles
Often ends in pool

22. Flow pattern

23. Tracing origin of blood spatter
A. Angle of Impact
B. Point of convergence
C. Point of origin
D. Source of spatter (type of weapon)

24. Blood Spatter (or splatter)
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

25. Dripping blood Can follow movement of victim and assailant
Can show the speed of blood loss.

26. 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
Determining Distance Blood Falls
Faster drop = larger diameter (size)
Higher distance = larger diameter
However, size of drop also depends on the volume of the drop.

27. Height Fallen
Single drops of blood falling from fingertip onto smooth cardboard from various heights.
No change in diameter beyond 7 ft.

28. Direction:Wave Cast-off
Tail of elongated stain
points in direction of travel .
Tail of wave cast-off points
back to parent drop
Parent drop
wave cast-off

29. Determining Direction of Blood
The angle of impact 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)
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)

30. Real World! Do the best you can!!!
What if blood drop is not a pretty oval?!?
Do the best you can!!!

31. Angle of Impact Gravitational dense zone at lower edge 90 80 70 60
50
40
Gravitational dense zone
at lower edge
20
30
10
Adapted from
Introduction to Forensic Sciences,
W. Eckert, CRC, 1997

32. 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
In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.
Low impact = beating
High impact = gunshot

33. Low Velocity velocity ≤ 5 ft/s
stain size is (relatively) large: diameter ≥ 4mm
examples: blood drops into blood and footstep spatters

35. Medium Velocity 5 ft/s ≤ velocity ≤ 25 ft/s
stain size : 1 mm ≤ diameter ≤ 4mm
examples: blood flicked off finger and blunt object used on victim

36. High Velocity velocity ≥ 100 ft/s ( 68 mph)
stain size (relatively small): diameter ≤ 1mm
examples: gunshots and propellers

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

40. Tracing Origin of Bloodspots uses
Point of convergence method
2 dimensional image
Point of origin method
adds 3rd dimension to image
In practice:
use of string & protractor at scene
use of computer at laboratory

41. Point of Convergence

42. Point of Convergence 17 5 ml blood squirted from a
syringe from height of 1 m
Point of Convergence

43. Point of Origin Origin Height above point of convergence
Distance from point of convergence
Height above point of convergence
Origin
length
width
Angle of impact = arc sin W/L
85
60
45
30

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

46. Gunshot Spatter
Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).
Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

47. Gunshot: back& forward spatter
Bloodstained foam held just above target surface.
Bullet passing L to R just above sheet
bullet exits foam
Bullet enters
foam
bullet
Back-spatter
on entry
Forward spatter
on exit

48. Types of Spatter Castoff Pattern = Blood flung off of swinging object.
Can reconstruct where assailant and victim were positioned.
Castoff Pattern = Blood flung off of swinging object.

49. Three overhead swings with hatchet

50. Example, cont’d
ceiling

51. Cast off Pattern (2/2) 1 2 3