1. Chapter 11 / 12 Recognition of Bloodstain Patterns

2. Recognition of Bloodstain Patterns
Bloodstain pattern analysis assists investigators in better understanding what took place at a specific crime scene.
It can assist in:
corroborating statements,
apprehending a suspect,
reconstructing past events,
and exonerate the accused

3. Properties of Human Blood
Blood is a fluid which circulates throughout body and transports oxygen, electrolytes, nourishment, hormones, vitamins and antibodies to tissues and organs
Composed of red blood cells (erythrocytes) and white blood cells (leukocytes), plasma and platelets

4. Properties of Human Blood
Blood is held together by strong cohesive molecular properties
These properties create surface tension within each drop and on external surfaces
Surface tension of blood is slightly less than that of water
Blood does not fall in tear drop configuration
Viscosity – mutual attraction of molecules of blood and the resistance to change of form or flow
Blood is six times more viscous than water
Specific gravity of blood is slightly higher than water

7. Properties of Human Blood
Blood falling through air increases velocity until force of air resistance that opposes the drop equals downward gravitational pull
at that point, it reaches terminal velocity
Estimate for maximum terminal velocity for free falling drop of blood was 25.1 ft per second.

8. Diameter of bloodstain is due to:
Function of volume of drop
The surface texture it impacts
Up to a point, the distance the blood falls.

11. Target Surface Considerations
Exposed blood has invisible outer skin referred to as surface tension
Blood will not break apart as falling through air unless an exterior force disrupts it
Hard smooth surfaces (glass, smooth tile) create little spatter
Wood or concrete create significant spatter

12. Size, Shape and Directionality
Geometry of bloodstains will generally allow for determination of their flight
Narrow end of elongated bloodstain usually points in direction of travel
After directionality has been determined, an area or point of convergence may be established by drawing straight lines through long axis of bloodstains

17. Size, Shape and Directionality
If angle of impact is 90 degrees, bloodstain is generally circular
Impact angles of less than 90 degrees generally result in elliptical bloodstains

18. Size, Shape and Directionality
Width and length of elliptical bloodstain allows you to calculate the angle of impact
Width is divided by length to produce a ratio number
Ratio is sine of impact angle: angle can be determined using a scientific calculator or sine function in trigonometric table

22. Spattered Blood
Defined as a random distribution of bloodstains that vary in size and that may be produced by a variety of mechanisms
Quantity of available blood can influence spatter
Amount of force applied also influences spatter

23. Spattered Blood Spattered blood is significant because:
Allows for determination of an area or location of the origin of blood source
If found on suspect’s clothing, may place person at scene of violent altercation
May allow the determination of the mechanism that created the pattern

25. Forward Spatter - gunshot

26. BackSpatter - gunshot

27. Horizontal Spatter - gunshot

28. Impact Spatter - beating

29. Impact Spatter – beating (horizontal)

30. Comparison A-gunshot, B- expirated blood, C- beating

31. Multiple drips (note satellite spatter).

32. Cast off - stabbing

33. Dried blood drop

34. Multiple drips

35. Expirated blood – blood in lungs

36. Arterial spurting

37. Knife blade

38. fingerprint

39. Smeared drop

40. Dried bloodstain – partially wiped away

41. Clotted spatter on fabric

42. Luminol enhanced footprint

43. Luminal enhancement of wiped up blood