1. Forensic Science
Forensic Serology

2. Composition of Blood
Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances
Main Components:
Erythrocytes = red blood cells (RBCs)
Leukocytes = white blood cells (WBCs)
Platelets = clotting factors
Plasma = the liquid part

3. 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

4. Antibodies in Blood Serum
ABO Blood System
Blood Type
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

5. 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 it does not have any antigens to cause agglutination

6. 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 factor affects blood donation compatibility
Rh+ blood types can accept either Rh+ or Rh-
Rh- can only accept Rh- blood or it will agglutinate

7. 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

8. (stop)
Blood Typing Lab

9. Blood Stain Analysis
Forensic Science

10. Testing for Blood Is it blood? Is it human blood? Whose blood is it?
When they find a red stain, investigators must ask themselves 3 questions:
Is it blood?
Is it human blood?
Whose blood is it?

11. Is it blood?
Presumptive tests (color tests) indicate the presence of blood
Kastle-Meyer: this solution of phenolphthalein turns bright pink when it encounters the blood protein hemoglobin
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

12. Is it blood?
Luminol: When sprayed on blood, this solution produces a faint blue light
This can work on blood that someone tried to clean up

13. (Luminol demos)

14. 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

15. 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.

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

17. 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

18. 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

19. 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

20. 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.

21. Lab: Affect of Height on Size of Blood Drops
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Lab: Affect of Height on Size of Blood Drops

22. 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

23. 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.

25. 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

26. 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.

27. area of convergence

28. 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

29. 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

30. 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!

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

32. 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”

33. 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

34. (stop)

35. Forensic Serology: Other Body Fluids

36. Other Body 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

37. 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

38. 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

39. (end)

40. 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