Chapter 11 / 12 Recognition of Bloodstain Patterns

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

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

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

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.

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.

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

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

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

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

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

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

Forward Spatter - gunshot

BackSpatter - gunshot

Horizontal Spatter - gunshot

Impact Spatter - beating

Impact Spatter – beating (horizontal)

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

Multiple drips (note satellite spatter).

Cast off - stabbing

Dried blood drop

Multiple drips

Expirated blood – blood in lungs

Arterial spurting

Knife blade

fingerprint

Smeared drop

Dried bloodstain – partially wiped away

Clotted spatter on fabric

Luminol enhanced footprint

Luminal enhancement of wiped up blood