Blood Spatter Flashcards
Blood Stain Pattern Analysis (BSPA)
Examination of the shapes, locations, and distribution patterns of bloodstains to provide an interpretation of the events which gave rise to their origin
Information obtained from BSPA (4)
Position of a victim
Evidence of a struggle
People/objects in the room (voids)
Confirm of refute statements about the actions of the crime scene
Why does blood tend to contract?
It has an “elastic-like” property caused by the forces of attraction between the molecules of the liquid (cohesion) - tends to resist penetration and separation, causing a perfect sphere
Maximum speed of blood and why
25 feet/second due to air resistance
Blood Patterns (6)
(PASS TP)
- Passive fall
- Arterial spurts or gushes
- Splashes/spatter
- Smears/transfers
- Trails
- Pools
Passive fall
Blood falling directly to the floor at 90 degrees will produce circular drops
What causes more satellites?
Textured surface
Arterial spurts or gushes
Typically found on walls or ceilings caused by pumping action of the heart
Splashes/spatter
Shaped like exclamation points, shape and position can help locate the position of the victim at the time of the attack
Smears/transfers
Left by the bleeding victim or other at the scene depositing blood as they touch or brush against a surface
Trails
Can be left by a bleeding victim depositing blood as they move from one location to another
Pools
Form around a victim that is bleeding heavily and remains in one place
Spines
Attached to the main droplet
Satellites
Not attached to the main droplet
Narrow/pointed end of a blood drop points…
in the direction of travel
Point of Convergence (POC)
Two dimensional position determining the origin of two or more drops of blood
Point of Hemorrhage (POH)/Point of Origin
Three dimensional position of where the blood originated
Steps of finding Point of Origin (3)
Find the POC
Find the angle of impact (AOI)
Find the POH
Angle of Impact (AOI)
Angle at which the blood hits the surface and determines the shape of the spatter drop – determines the length of the drop
AOI Equation
sinAOI = width/length AOI = inverse sin (width/length)
POH equation definitions: x and d
x = the POH, the hight above POC (opposite) d = length from center of blood drop to POC (adjacent)
POH Equation
tanAOI = x/d x = tanAOI (x) d
Why is the POH overestimated?
Blood falls in an arch due to air resistance and gravity
Low Velocity Drops (speed, size, how)
5 feet/second
Larger stains, 4mm and greater
Dripping blood, off knife, arms swinging, hit with rock
Medium Velocity Drops (speed, size, how)
25 feet/second
1-4 mm
Hit with fist, knife, bat, club - longer blunt objects
High Velocity Drops (speed, size, how)
More than 100 feet/second (mist)
Smaller than 1mm
High velocity guns
Cast-off Spatter
Results when an object swung in an arc flings blood onto nearby surfaces
What cast-off spatter can tell us (4)
Direction of swinging object
Velocity of object
Left or right handed
Minimum number of blows
Back Spatter
Arises from the entrance wound and moves towards the weapon; most common with high velocity shot guns; can leave blood on the gun or shooter
Higher velocity leads to _____ back spatter
more
Skeletonization
Occurs when the edges of a stain dry to the surface; typically occurs within 50 seconds
