Download Bloodstain Patterns

BLOODSTAIN PATTERNS
BLOOD COMPONENTS
Plasma
• 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 BLOOD
Examples:
• 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 Spatter
Medium Velocity Spatter
• Generally size range 1-3 mm in diameter
Castoff Bloodstain Patterns
Low Velocity Spatter
• Blood flung from object – such as bat or knife
Passive Bloodstains
Low 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