How is Blood Evidence used in Forensics?

1. How is Blood Evidence used in Forensics?

2. How blood evidence is collected • 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. • Small object, send whole object in. • Large object, cover with paper and tape down or scrape it off with a knife. • 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?) 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

6. Presumptive Screening Tests Kastle-meyer - Phenolphthalein • Color test - Positive result = pink • Still used today • Used on dried blood 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

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

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 • 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. ABO Markers

12. Blood Group Markers ABO Markers (antigen and antibodies)

13. Blood Group Markers ABO Markers (antigen and antibodies)

14. Blood Group 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 = + ABO Markers

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.

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

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

31. 80 90 10 60 50 40 70 20 30 Angle of Impact Gravitational dense zone at lower edge 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

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

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

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

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).

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

49. Three overhead swings with hatchet

50. Example, cont’d ceiling