Blood stain patterns


				*FORENSIC BIOLOGY 101* *Blood stain patterns*



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The success or failure of any criminal investigation often depends on the recognition of physical evidence left at the crime scene and the proper analysis of that evidence.

Crime scenes that involve bloodshed often contain a wealth of information in the form of bloodstains. The pattern, size, shape, and the location of such stains may be very useful in the reconstruction of the events that occured.

WILLIAM G. ECKERT and STUART H. JAMES

The is an example of Transfer bloodstain.

In blood analysis stain patterns can play a very distinct and important role. It

identifies where themurder could have taken place and what instrument was

used to accomplish that task.Blood spatters can be divided into three mian

categories: Transfer, Passive, and Projected. A transfer blood stain is created

when a wet, blood surface comes into contact with a secondary surface. Some

examples are: contact bleeding, swipe or smear, wipe or smudge. Passive

bloodstains are drops created or formed by the force of gravity acting alone.

Some examples are drops, drip patterns, pools and clots Projected blood stains are created when an

exposed blood source is subjected to an action or force greater than the force of gravity. Forces applied

by the object determines the size, shape and the number of stains that result.

This is an example of Passive bloodstain.

An example of Projected Bloodstain

The type of surface the blood strikes affects

the amount of resulting spatter, including the

size and the appearance of the blood drops.

Next investigators look at the surface texture.

The harder the surface, the less splater results.

As well, the direction of travel is examined.

The pointed end of a bloodstain always faces its direction of travel. The impact

angle of blood on a flat surface can also be determined by measuring the degree of circular distortion of the

stain. As the angle decreases, the stain becomes elongated in shape. The origin of a blood spatter in a

two-dimensional configuration can be esablished by drawing straight line through the long axis of several

individual bloodstains. Furthermore investgators look for the intersection or point of covergence of the lines

which represents the point from which the blood emanated. All these elements allow investgators to have a

greater and more throrough knowledge of the crime scene and the crime that had been commited.