1. Forensic Blood Evidence
Forensic Science
Unit 8B

2. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

3. 1. Composition of Blood
Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances
Main Components of Blood:
Plasma = 55%; the liquid part; mostly water; suspends (floats) all the other cells etc. in blood.
Erythrocytes = red blood cells (RBCs); carry oxygen
Leukocytes = white blood cells (WBCs); fight diseases
Platelets = blood clotting factors; help with healing
Proteins/other chemicals = various functions; very small

4. 1. Composition of Blood

5. 1. Blood: Antigens and Antibodies
Antigens: proteins on surface of cells (including RBCs) that identify them
Different types of cells have different antigens
Antibodies: Y-shaped immune system proteins that recognize and bind to foreign objects to neutralize them
You get vaccines to develop these!
Agglutination: clumping of antibodies when they bind to their specific antigen

6. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

7. 2. Blood Types
Different blood types are based on the different antigens on the surface of red blood cells (RBCs).
There are more than 15 different blood typing systems, but the ABO and Rh systems are the most commonly used.

8. 2. Blood Types: ABO Blood System
The ABO system considers two main antigens on RBCs: A and B.
Therefore, there are 4 different possible major blood types:
A (only A antigens present)
B (only B antigens present)
AB (both A and B antigens present
O (no antigens present)

9. 2. Blood Types
Blood type is usually tested through antibody-antigen tests.
If blood is exposed to an antigen that it identifies as “foreign”, the antibodies in that blood will agglutinate (“clump around”) the foreign antigens. This agglutination (“clumping”) visible in the laboratory.
This is an important factor in blood donations: a person’s body will reject blood with different RBC antigens.

10. 2. Blood Types
The concept of specific antigen–antibody reactions has been applied to other immunoassay techniques for the detection of drugs of abuse in blood and urine.

11. 2. Blood Types: ABO Blood System

12. 2. Blood Types: ABO Blood System
Antigens on RBCs
Antibodies in Blood Serum A
anti-B B
anti-A AB
A and B
none O
anti-A and anti-B
Anti-A antibodies will agglutinate (clump) in Type A blood
Anti-B antibodies will agglutinate in Type B blood
Type AB blood will agglutinate in anti-A or anti-B serum
Type O blood will not cause agglutination

13. 2. Blood Types: Blood Donors and Recipients
BLOOD TYPE DONATES TO RECEIVES FROM
A A, AB A, O
B B, AB B, O
AB AB A, B, AB, O
O A, B, AB, O O
Type AB blood is the universal recipient because it can take any of the 4 types and not agglutinate
Type O (most common) is the universal donor beacuse it does not have any antigens to cause agglutination

14. 2. Blood Types: Blood Donors and Recipients

15. 2. Blood Types: Rh Factor
Rh (Rhesus) factor is another important blood antigen
This is the positive (+) and negative (-) of blood types
Rh- means you don’t have the antigen
Rh+ means you do have the antigen
Rh factor affects blood donation compatibility
Rh+ blood types can accept either Rh+ or Rh-
Rh- can only accept Rh- blood or it will agglutinate

16. 2. Blood Types: Genetics of Blood
Blood types are determined by looking at 2 inherited genes (one from each parent)
There are 3 common alleles for blood types: A, B, and O, with 6 possible combinations
BLOOD TYPE ALLELE COMBINATIONS
A AA, AO
B BB, BO
AB AB
O OO
Punnett Square

17. 2. Blood Types: Most Common Types in the United States

18. 2. Blood Types: Most Common Alleles in each Native Population

19. 2. Blood Types: Most Common Alleles in each Native Population

20. 2. Blood Types: Most Common Alleles in each Native Population

21. Lab 8B.1 Forensic Blood Typing

22. Blood Stain Analysis

23. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

24. Blood Stain Analysis: Testing for Blood
When they find a red stain, investigators must ask themselves three questions:
Is it blood?
Is it human blood?
Whose blood is it?

25. 3A. Is it blood?
Presumptive tests (color tests) indicate the presence of blood
Kastle-Meyer: this solution of phenolphthalein (an acid/base indicator) turns bright pink when it encounters the blood protein hemoglobin. (Blood is slightly basic: pH ~7.4)
Some vegetable matter like potatoes and horseradish can give a positive K-M result, but… you’re probably not going to find those at a crime scene

26. 3A. Is it blood?
Luminol: When sprayed on blood, this solution produces a faint blue light.
Used to find trace amounts of blood at crime scenes.
This can work on blood that someone tried to clean up

27. Video Clip
Luminol (2.32 min):

28. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

29. 3B. Is it human or animal blood?
Precipitin Test
Serum made in rabbit contains antibodies against human blood
Crime scene blood is layered on top of the anti-human serum in a test tube
If the sample is positive for human blood, a cloudy precipitate will form where the 2 layers meet

30. 3. Whose blood is it?
A DNA analysis would have to be performed to find out exactly who the blood belongs to
But ABO blood typing can narrow down a pool of suspects.

31. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

32. Blood Spatter Analysis
Passive Dripping
Transfer
Impact Spatter:
Occurs when an object impacts a source of blood

33. 4. Blood Spatter Analysis
Blood spatter patterns can be used to re-create a crime scene. It is possible to determine:
The direction the blood was travelling
The angle of impact
The point of origin of the blood
This can help determine the manner of death
Where did the blood come from?
What caused the wounds?
From what direction was the victim wounded?
How were the victim(s) and perpetrator(s) positioned?
What movements were made after the bloodshed?
How many potential perpetrators were present?
Does the bloodstain evidence support or refute witness statements?

34. 4. Blood Spatter Analysis – Type of Spatter
Blood spatter is categorized as either:
Impact spatter - created when a force is applied to a liquid blood source
Projection spatter – caused by arterial spurting, expirated spray or spatter cast off an object
The characteristics of blood spatter depend on:
Speed at which the blood leaves the body
Type of force applied to the blood source.

35. 4. Blood Spatter Analysis – Type of Stains
Bloodstains are classified into three basic types:
Passive stains – Include drops, flows and pools, and typically result from gravity acting on an injured body.
Transfer stains – result from objects coming into contact with existing bloodstains and leaving wipes, swipes or pattern transfers behind such as a bloody shoe print or a smear from a body being dragged.
Projected or impact stains – result from blood projecting through the air and are usually seen as spatter, but may also include gushes, splashes and arterial spurts.

36. 4. Blood Spatter Analysis – Type of Stains: Transfer Pattern

37. 4. Blood Spatter Analysis – Type of Stains

38. 4. Blood Spatter Analysis - Surface
When examining blood spatter, is it important to consider the surface
Hard and nonporous surfaces like glass and tile generally result in round drops with less spatter
Rough surfaces like carpeting, wood, or fabric usually result in irregularly shaped stains with serrated edges and possibly satellite spatter
Satellite spatter are the tiny droplets that break away from the main drop

39. 4. Blood Spatter Analysis - Surface

40. 4. Blood Spatter Analysis - Speed
Size of blood drops tells us about the speed of the drop upon impact
Small droplets (less than 1 mm; spray) mean high velocity around 100 ft/s
Example: gunshot wound
Medium droplets (1-4 mm) mean medium velocity around 25 ft/s
Example: stabbing
Large droplets (4-6 mm) mean low velocity around 5 ft/s
Example: blunt object impact such as a hammer to the head

41. 4. Blood Spatter Analysis – Speed Backspatter from a gunshot wound on a car steering wheel

42. 4. Blood Spatter Analysis - Height
How far from the ground a blood drop originated is reflected in the size of the blood drop.
A drop from farther up will spread out more upon impact.

43. 4. Blood Spatter Analysis - Direction
Momentum tends to keep blood moving the direction it was traveling
In an elongated blood drop, the tail points in the direction of the blood’s movement
Satellite droplets appear in front of the moving droplet of blood
direction of movement

44. 4. Blood Spatter Analysis - Direction

46. 4. Blood Spatter Analysis - Angle
angle = arcsin (width/length)
The angle of impact can be found mathematically
Divide the width (shorter side) of the blood drop by the length (longest part)
Then take the inverse sin, also called “arcsin” or “sin-1”of that number to get the angle.

48. 4. Blood Spatter Analysis - Angle
The smaller the angle (meaning the source was closer to the floor) the longer and more stretched the blood drop looks

49. 4. Blood Spatter Analysis - Convergence
You can figure out where blood came from by drawing lines through the long axis of the droplet.
Remember the tail (and satellites) indicate the direction blood was moving, so the origin is the opposite direction.
Where lines meet is called the area of convergence.

50. area of convergence

51. 4. Blood Spatter Analysis – Origin
Lines of convergence give you a direction that blood came from, but not height.
You can use the angle of impact and trigonometry to determine how far up the blood came from

52. tanθ = height/distance to convergence so height = tanθ x distance
Remember SOH CAH TOA
Tangent is opposite/adjacent
tanθ = height/distance to convergence
so height = tanθ x distance
height = tan27° x 5.75 ft
height = x 5.75 ft
height = ~2.9 ft above the ground
angle
opposite
hypotenuse
adjacent
Yay math!

53. 4. Blood Spatter Analysis - Origin
Use angle of impact and convergence lines to make an imaginary right triangle
You know the angle of impact, you know the “adjacent” side length
Solve for height using the Law of Tangents

54. Add this formula to your notes…
To find the height of the origin of blood spatter… height = tanθ x distance to convergence

55. 4. Blood Spatter Analysis - Origin
DEXTER
You can use string to help you recreate point of origin
There are also computer programs to help
“No More Strings”

56. 4. Blood Spatter Analysis: Patterns
Characteristics
Gunshot spatter
Characterized by both forward spatter from the exit wound and back spatter from an entrance wound.
Back Spatter
Affected by location of injury, size of wound, and distance between victim and muzzle.
Cast-off
Created when a blood-covered object flings blood in an arc onto a nearby surface.
Arterial Spray Spatter
When a victim suffers an injury to an artery or to the heart, the pattern shows large spurted stains for each time the heart pumps.
Expiated Blood Pattern
Created by blood that is expelled form the mouth or nose form an internal injury.
Void
When an object blocks the deposition of blood spatter onto a surface.
Flow
Drops or large amounts of blood flowing due to the pull of gravity
Pools
When blood collects in a level and undisturbed place
Skeletonization
When the edges of a stain dry to the surface
Trail
A series of drops separate from other patterns, formed by blood dripping off of an object or an injury.

57. 4. Blood Spatter Analysis: Patterns

58. 4. Blood Spatter Analysis: Patterns

59. 4. Blood Analysis – Wrap Up
Ask:
Is it blood?
Is it human blood?
Whose blood is it?
Figure out:
Speed of impact
Angle of impact
Area of convergence
Point of origin
CLASS CHARACTERISTICS:
species
blood type
Rh factor
diseases?
INDIVIDUAL CHARACTERISTICS
DNA profile

60. Forensic Serology: Other Bodily Fluids

61. Unit 8B: Forensic Blood Evidence – Contents
Blood Types
Blood Stain Analysis
Is it blood?
Is it human or animal blood?
Blood Spatter Analysis
Other Bodily Fluids

62. 5. Other Bodily Fluids: Saliva
Consists of water, mucin for lubrication, amylase enzyme for digestion, buccal (cheek) cells that could provide DNA
Saliva is often associated with sexual assaults and bite mark evidence
Presumptive tests for saliva check for the amylase enzyme

63. 5. Other Body Fluids: Semen
Consists of water, spermatozoa, enzymes, salts
Semen is often evidence in sexual assault cases
Presumptive tests for semen include
Black light fluorescence
Chemical test for acid phosphatase (enzyme from prostate), turns purple when present
Confirmatory tests include microscopic examination for presence of sperm
DNA analysis can individualize the sample

64. 5. Other Body Fluids: Urine
Urine is composed mostly of water, and also includes urea (nitrogenous compound) and salts.
Urine is most often used for the detection of drugs in the body
EMIT (Enzyme-Multiplied Immunoassay Technique) test reveals the presence of specific drugs through antibody binding

65. 5. Other Body Fluids: Rape Evidence
The rape victim must undergo a medical examination as soon as possible after the assault.
At that time the appropriate items of physical evidence including clothing, hairs, and vaginal and rectal swabs can be collected for subsequent laboratory examination.
All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags.
Bedding, or the object upon which the assault took place, may also be carefully collected.

66. 5. Other Body Fluids: Rape Evidence
If a suspect is apprehended within 24 hours of the assault, it may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect.
Items routinely collected from the suspect include all clothing, pubic hair, head hair, penile swab, and a blood sample or buccal swab for DNA typing.
The forceful physical contact between victim and assailant may result in a transfer of such physical evidence of blood, semen, saliva, hairs, and fibers.

67. Resources
, Saferstein, Richard. Forensic Science: An Introduction. New Jersey: Pearson Prentice Hall, 2011.
, Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 8th ed. Upper Saddle River, NJ; Pearson Prentice Hall, 2004.
Sam Sheppard by Fred McGunagle