Forensic Blood Evidence

1. Forensic Blood Evidence Forensic Science Unit 8B

2. Unit 8B: Forensic Blood Evidence – Contents • Blood • 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 • 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 • 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 TYPEDONATES TORECEIVES FROM A A, AB A, O B B,AB B, O AB ABA, 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 TYPEALLELE 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 • 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. 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 3A. Is it blood?

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): https://www.youtube.com/watch?v=KWhRvALk-Qo

28. Unit 8B: Forensic Blood Evidence – Contents • Blood • 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 • 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

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 – SpeedBackspatter 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 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. angle = arcsin (width/length)

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