Chapter 11 / 12Recognition of Bloodstain

Patterns

Recognition of Bloodstain Recognition of Bloodstain PatternsPatterns

• Bloodstain pattern analysisBloodstain pattern analysis assists assists investigators in better understanding what investigators in better understanding what took place at a specific crime scene. took place at a specific crime scene.

• It can assist in: It can assist in: – corroborating statements, corroborating statements, – apprehending a suspect, apprehending a suspect, – reconstructing past events, reconstructing past events, – and exonerate the accusedand exonerate the accused

Properties of Human BloodProperties of Human Blood

• Blood is a fluid which circulates throughout Blood is a fluid which circulates throughout body and transports oxygen, electrolytes, body and transports oxygen, electrolytes, nourishment, hormones, vitamins and nourishment, hormones, vitamins and antibodies to tissues and organsantibodies to tissues and organs

• Composed of red blood cells Composed of red blood cells (erythrocytes) and white blood cells (erythrocytes) and white blood cells (leukocytes), plasma and platelets(leukocytes), plasma and platelets

• Blood is held together by strong cohesive molecular Blood is held together by strong cohesive molecular propertiesproperties– These properties create surface tension within each drop and on These properties create surface tension within each drop and on

external surfacesexternal surfaces– Surface tension of blood is slightly less than that of waterSurface tension of blood is slightly less than that of water– Blood does not fall in tear drop configurationBlood does not fall in tear drop configuration

• Viscosity – mutual attraction of molecules of blood and Viscosity – mutual attraction of molecules of blood and the resistance to change of form or flowthe resistance to change of form or flow– Blood is six times more viscous than waterBlood is six times more viscous than water

• Specific gravity of blood is slightly higher than waterSpecific gravity of blood is slightly higher than water

Properties of Human BloodProperties of Human Blood

Properties of Human BloodProperties of Human Blood

• Blood falling through air increases velocity Blood falling through air increases velocity until force of air resistance that opposes until force of air resistance that opposes the drop equals downward gravitational the drop equals downward gravitational pull . . . pull . . . – at that point, it reaches at that point, it reaches terminal velocityterminal velocity

• Estimate for maximum terminal velocity for Estimate for maximum terminal velocity for free falling drop of blood was 25.1 ft per free falling drop of blood was 25.1 ft per second. second.

Diameter of bloodstain is due to:Diameter of bloodstain is due to:

– Function of volume of dropFunction of volume of drop

– The surface texture it impactsThe surface texture it impacts

– Up to a point, the distance the blood Up to a point, the distance the blood falls.falls.

• Exposed blood has invisible outer skin Exposed blood has invisible outer skin referred to as surface tensionreferred to as surface tension

• Blood will not break apart as falling Blood will not break apart as falling through air unless an exterior force through air unless an exterior force disrupts itdisrupts it

• Hard smooth surfaces (glass, smooth tile) Hard smooth surfaces (glass, smooth tile) create little spattercreate little spatter

• Wood or concrete create significant Wood or concrete create significant spatterspatter

Target Surface ConsiderationsTarget Surface Considerations

Size, Shape and DirectionalitySize, Shape and Directionality

• Geometry of bloodstains will generally Geometry of bloodstains will generally allow for determination of their flightallow for determination of their flight

• Narrow end of elongated bloodstain Narrow end of elongated bloodstain usually points in usually points in direction of traveldirection of travel

• After directionality has been determined, After directionality has been determined, an area or point of convergence may be an area or point of convergence may be established by drawing straight lines established by drawing straight lines through long axis of bloodstainsthrough long axis of bloodstains

• If angle of impact is 90 If angle of impact is 90 degrees, bloodstain is degrees, bloodstain is generally circulargenerally circular

• Impact angles of less Impact angles of less than 90 degrees than 90 degrees generally result in generally result in elliptical bloodstainselliptical bloodstains

Size, Shape and DirectionalitySize, Shape and Directionality

Size, Shape and DirectionalitySize, Shape and Directionality

• Width and length of elliptical bloodstain Width and length of elliptical bloodstain allows you to calculate the angle of impactallows you to calculate the angle of impact

• Width is divided by length to produce a Width is divided by length to produce a ratio numberratio number

• Ratio is sine of impact angle: angle can be Ratio is sine of impact angle: angle can be determined using a scientific calculator or determined using a scientific calculator or sine function in trigonometric tablesine function in trigonometric table

• Defined as a random distribution of Defined as a random distribution of bloodstains that vary in size and that may bloodstains that vary in size and that may be produced by a variety of mechanismsbe produced by a variety of mechanisms– Quantity of available blood can influence Quantity of available blood can influence

spatterspatter– Amount of force applied also influences Amount of force applied also influences

spatterspatter

Spattered BloodSpattered Blood

• Spattered blood is significant because:Spattered blood is significant because:

– Allows for determination of an area or location Allows for determination of an area or location of the origin of blood sourceof the origin of blood source

– If found on suspect’s clothing, may place If found on suspect’s clothing, may place person at scene of violent altercationperson at scene of violent altercation

– May allow the determination of the May allow the determination of the mechanism that created the patternmechanism that created the pattern

Spattered BloodSpattered Blood

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