Blood Patterns

The interpretation of blood patterns is the reconstruction aspect of forensic blood analysis. It is distinct from identification, species testing, and DNA analysis. During violent events blood can drip from a source, or it can be spattered onto floors, walls, and objects. The patterns the blood forms on the surfaces can help a forensic scientist know what type of event caused the blood to spatter in the first place, how much energy was involved, and possibly something about the direction of a moving source and the angles at which blood droplets hit the surfaces.

Blood patterns at crime scenes are important sources of information about the events that took place there. If there is a possibility that more than one person was bleeding, the laboratory analyzes specimens of the dried blood, first, to make sure it is blood; then, to make sure it is human; and finally, to analyze its DNA profile. Blood patterns will have different meanings if there is more than one blood source. As a result the identification and individualization steps in blood analysis always precede the reconstruction step.

Analysis and DNA Typing of Blood and Other Physiological Fluids

Once established as human, blood and physiological fluid stains and traces are next DNA typed to find out who may have deposited them. DNA profiling means finding out the DNA types at several different genetic loci.

Genetic loci, or different locations on the DNA, are explained later in the book. The combined set of types at the different locations is the profile. It is the profile that is actually characteristic of an individual.