Bloodstains and Patterns

Bloodstains and bloodstain patterns are often the subject of forensic science testimony in assault or homicide cases. Initially, the investigative question can simply be whether a particular stain is blood or not. Preliminary and laboratory tests are available to determine if a stain is blood. More complex is the question of what conclusions can be drawn from a pattern of bloodstains or spattering. Patterns from the spattering of blood have been used to form the basis for testimony about such issues as the sequence of events, the distance from which a victim was shot, claims of self-defense, and any number of other homicide or assault dynamics. It may include the determination of whether a stain resulted from arterial spurting, blood dripping, aspirated (coughed) blood, back spatter, angular deposits, flight paths, or many other characteristics of the blood path that led to the recorded bloodstain pattern. Such an analysis involves complicated and technical issues of fluid dynamics. Unfortunately, untrained police witnesses without any training in fluid dynamics often purport to offer conclusions about the patterns that do not meet admissibility requirements.