Bloodstain Pattern Analysis & Blood Evidence

ADJ13 Criminal Investigations

Bloodstain Pattern Analysis

Bloodstain pattern analysis (BPA) is the interpretation of bloodstains in a forensic capacity to recreate the actions that caused the bloodshed.

Analysis uses principles of biology (behavior of blood), physics (cohesion, capillary action, velocity), and mathematics (geometry, distance, angle).

A Little Bit About Blood…

Blood consists of both liquids and solids.Liquids: Serum and plasma

Solids: Red and white blood cells, platelets, proteins

Absent hemophilia, blood clots relatively soon after exposure to oxygen, dependent upon the amount exposed and timing.

Blood will leave the body in many different ways: flow, drip, spray, spurt, gush, ooze…

3 Types of Bloodstains

3 Basic Types:

Passive BloodstainsControlled by gravity. Blood generally observed in drips, flows, and pools.

Transfer BloodstainsGenerally observed in wipes, swipes, pattern transfers.

Projected/Impact BloodstainsGenerally observed in spatter, gushes, splashes, and arterial spurts.

Passive Bloodstains

Created or formed by the force of gravity acting alone.

Bloodstain Directionality

Bloodstain Directionality

Transfer Bloodstains

Created when a bloody surface comes into contact with another surface.

Easy example of Locard’sTransfer Principle.

Transfer Bloodstains

Transfer Bloodstains

Projected/Impact Bloodstains

Blood Spatter

Generally split into two different types:Impact Spatter

Force applied

Projection SpatterArterial spurts, expirated spray, spatter cast off object

Arterial Spurt

Expirated Spray

Spatter Cast Off

Gunshot Spatter

Can vary dependent upon the caliber of the firearm, place of the wound, location of exit wound, distance between firearm and victim.

Typically, forward spatter is a fine mist and back spatter consists of larger, and fewer, blood drops.

Bloodstain Void

Demonstrates presence of object

Investigator must be able to account for any and all objects on scene; absence of an object with a presence of bloodstain void means the scene has been tampered with, staged, or suspect(s) removed item.

Blood EvidenceCrime scenes with bodily injury are likely to have blood evidence.

The type of injury, amount of force, and type of weapon used determine the volume and pattern of the blood evidence.

Sharp Force Injuries: smaller surface area, less blood transfer to weapon, smaller and more linear pattern of bloodstains.

Blunt Force Injuries: larger surface area, generally larger weapons used, varying size of bloodstain drops.

Blood Evidence: Drop Angle Physics