Blood Spatter

Blood spatter patterns

Help to reconstruct the series of events surrounding a shooting, stabbing or beating

First reference to blood spatter analysis was in 1894

Blood spatter evidence was used by the defense in the Sam Shepard case in 1955 to help exonerate him.

Blood Spatter patterns

Makes it possible to determine:

– the direction the blood was traveling

– the angle of impact

– the point of origin of the blood

– The manner of death, based on blood velocity

Blood drops

Blood is a thick mixture of blood cells and plasma

When a person is bleeding, gravity acts on blood, pulling it downward, making it longer than it is wide

Blood is cohesive, so it “sticks together” and doesn’t separate as it falls

Blood maintains a round appearance when it falls on a flat surface

Satellites

Small secondary droplets that have overcome the force of cohesion and separated from the main droplet of blood

Six Patterns of Blood Spatter

1. Circular Drops – produced by blood falling directly to the floor at a 90 degree angle

- secondary satellites will be produced if the surface is textured

- this is known as passive fall

Patterns (continued)

2. Arterial spurts or gushes found on walls or ceilings

- caused by the pumping action of the heart

Patterns (continued)

3. Splashes – shaped like exclamation points.

- the shape and position of the spatter pattern can help locate the position of the victim at the time of attack

Patterns (continued)

4. Smears – left by a bleeding victim depositing blood as he or she touches or brushes against a wall or furniture

Patterns (continued)

5. Trails – left by a bleeding victim as they move from one location to another

- droplets could be round or smeared or even appear as spurts

Patterns (continued)

6. Pools of blood – form around a victim who is bleeding heavily and remains in one place

More Patterns

Fine mist – produced by high velocity impact, like a gunshot wound

Low velocity pattern – produced by a beating with a pipe

Voids – empty spaces in a spatter pattern that help determine if something was moved after the attack

Examination of Directionality of Blood

The shape of an individual drop of blood can provide important clues in an investigation.

As moving blood strikes a surface, several forces affect the droplet of blood:

– Cohesion – force between two similar substances

– Adhesion – force between two unlike surfaces

– Surface tension – an elastic characteristic along the outer edge of a liquid casued by the attraction of like molecules

Lines of Convergence The location from which the blood originated can be

determined if there are at least two blood spatters.

Draw straight lines down the long axis of the blood spatter and note where the lines intersect – this indicates the lines of convergence

Crime Scene Investigation of Blood

Even after washing a room of visible blood, some blood evidence remains

Luminol – causes hemoglobin (the iron containing portion of the blood) to fluoresce under black light

Steps in Investigating Blood left at a Scene

1. Confirm the stain is blood

2. Confirm that the blood is human blood

3. Determine the blood type

4. Perform a DNA analysis if necessary and if DNA can be isolated from the sample