BLOODSTAIN PATTERNS

BLOOD COMPONENTSPlasma• fluid portion of normal unclotted blood • red blood cells, white blood cells, and

platelets are suspended in it

BLOOD COMPONENTS

Serum• liquid portion of clotted blood

SURFACE TENSION OF BLOOD

• held together by strong cohesive molecular forces

• “outer skin”• Surface tension lightly less that that of water• Liquid mercury is about 10x greater • Blood does not fall in teardrop configuration

SURFACE TENSION

• To create splatters, an external force must overcome surface tension of blood

SURFACE TENSION

Surfaces• Generally, clean glass or smooth tile, very little

splatter• Rough texture, wood or concrete, significant

splatter

GEOMETRY OF BLOODSTAIN

• Can determine direction of flight by examining edge characteristics

GEOMETRY

Angle of impact 90 degrees • results in circular shape

GEOMETRY

Angle of impact Less than 90 degrees

• Elongated

GEOMETRY

• If you measure width & length of an elliptical bloodstain you can calculate angle of impact

• Divide width by length • take sin-1 • gives angle of impact

Geometry

• Once get angle of impact for each bloodstain• 3D origin may be determined

DIRECTION OF TRAVEL

• Narrow end of elongated blood stain points in direction of travel

SPATTERED BLOOD

• random distribution of bloodstains that vary in size that may be produced buy a variety of mechanisms

SPATTERED BLOODExamples:• Gunshot• Beating• Stabbing• power tools• Arterial• cast-off• passive

SPATTERED BLOOD

• may allow determination of an area • or location of origin of blood source

SPATTERED BLOOD

• If found on a suspect’s clothing, it may place that person at scene of violent altercation

SPATTERED BLOOD

• May allow determination of mechanism by which pattern was created

SIZE, QUANTITY AND DISTRIBUTION OF SPATTER DEPENDS ON

• Quantity of blood subjected to impact• Force of impact• Texture of surface impacted by blood

GUNSHOT

• High Velocity Spatter• Misting effect• Varying sizes of impact spatters• Depend of caliber of weapon, location,

number of shots, etc.

Gunshot

EXAMPLE BACK SPATTER

EXAMPLE GUNSHOT IMPACT SPATTER

Beating and Stabbing Impact SpatterMedium Velocity Spatter

• Generally size range 1-3 mm in diameter

Castoff Bloodstain PatternsLow Velocity Spatter

• Blood flung from object – such as bat or knife

Passive BloodstainsLow Velocity

• Blood dripping from injured person

What happens when blood hits blood?

• Drip patterns

Large Volume Bloodstains

• Splashing and ricochet• Often from victim with large wound or

vomiting

EXPIRATED BLOODSTAIN PATTERNS

• Blood accumulates in lungs, sinuses, airway passages of victim

• Forcefully expelled from living victim• Can look similar to other bloodstain patterns• can only be explained if victim has blood on

face

ARTERIAL BLOODSTAIN PATTERNS

• Can be very large gushing or spurting patterns to very small spray types

OTHER BLOODSTAIN PATTERNS

• Transfer bloodstain patterns• Altered bloodstains• Void areas or patterns

INTERPRETATION OF BLOODSTAINS ON CLOTHING AND FOOTWEAR

• Whose blood is it?• How did it get there?

LUMINOL

• Used for latent bloodstains at crime scene

CHALLENGES

• Bloodstain pattern interpretation can be very complex

Need solid grasps of:• Mathematics• Physics• scientific method• practical experience