Blood Spatter

Blood spatter, or bloodstain pattern interpretation, is a technique that seeks to piece together the events that caused bleeding. Knowing how the blood got on the wall or other surface can be helpful in determining if a crime was committed and if the blood is evidence in that crime.

The blood spatter pattern can tell a trained investigator much about what crime may have been committed and rule out other types of crime. Together with other evidence, blood spatter can be very useful in piecing together what took place, identifying the victim, and determining who was responsible.

One of the first things that a forensic investigator needs to do when examining a blood spatter is to verify that the material is indeed blood. This can be determined by using tests that are portable enough to be used right at the scene. Later, tests will be done to determine if the blood is animal or human in origin and even to narrow down the people from whom the blood may have come.

In the actual spatter analysis, a forensic investigator determines the trajectory of the blood (where the blood came from and how it spread over the surface). By measuring the shape of the bloodstain on a surface, the direction of movement can be determined. As well, the speed at which the blood contacted the surface can be approximated. This can help distinguish, for example, between the rapid movement of blood that can be produced by a gunshot or the severing of an artery in opposition to the slower movement of blood from a minor cut.

If blood originated some distance away from a surface, the force of impact will cause the blood to break up into smaller drops. Thus, a blood spatter consisting of larger drops with a trail of smaller drops can tell an investigator much about how the blood got there and where the blood came from (i.e., near the floor, higher up in a room, near or far away from the surface).

The trained eyes of an experienced investigator remain one of the most powerful tools in blood spatter analysis. Specialized analytical computer programs are also available. Such detailed analysis can be important if the blood spatter is presented as evidence in a legal case.

see also Bloodstain evidence; Cast-off blood; Crime scene investigation.