Blood patterns at a crime scene

Why it is important A basic understanding of blood spatter analysis allows first responding officers and investigators alike to assist in correctly collecting and preserving bloodstain data at the scene.

Bloodstain pattern categories Passive bloodstains Passive bloodstains are those stains created by the force of gravity. Projected bloodstains A projected stain occurs when some form of energy has been transferred to a blood source. Transfer/Contact bloodstains A transfer or contact stain is produced when an object with blood comes in contact with an object or surface that does not have blood. It may be possible to discern the object that left the blood impression.

PASSIVE TRANSFER PROJECTED

Blood spatter patterns Low velocity impact spatter Objects traveling less than 1.5 m/s come in contact with a blood source, stains generally larger than 3 mm in diameter. Medium velocity impact spatter Objects traveling between 1.5 m/s and 7.5 m/s come in contact with a blood source, stains is generally between 1 mm and 3 mm in diameter. Ex: blunt force trauma or cutting/stabbing actions. High velocity impact spatter Objects traveling greater than 30 m/s come in contact with a blood source, stains are generally smaller than 1 mm in diameter. Ex: gunshots or explosives, but may also be caused by industrial machinery, coughing, or sneezing.

Low velocity Medium velocity High velocity

Directionality patterns

Point of convergence By drawing a line through the long axis of a group of bloodstains the point of convergence can be determined.