Why and when is bloodstain pattern analysis used?
Bloodstain evidence is most often associated with violent acts such as assault, homicide, abduction, suicide or even vehicular accidents. Analyzing the size, shape, distribution, overall appearance and location of bloodstains at a crime scene helps investigators by answering basic questions including:
- What occurred?
- Where did the events occur?
- Approximately when and in what sequence?
- Who was there? Where were they in relation to each other?
- What did not occur?
One of the most important functions of bloodstain pattern analysis is to support or corroborate witness statements and laboratory and post-mortem findings. For example, if the medical examiner determines the cause of death is blunt force trauma to the victim’s head, the pattern and volume of blood spatter should be consistent with a blunt instrument striking the victim one or more times on the head. Conversely, if the spatter resembles that seen in expirated blood spray, the analyst will check the medical examiner or pathologist reports for injuries that can cause the presence of blood in the nose, throat or respiratory system of the victim. If blood is not reported in these locations, the analyst may be able to exclude expiration as the possible cause of that spatter pattern.