Blood Spatter Interpretation at Crime and Accident Scenes: A Basic Approach
Akin, Louis L., The FBI Law Enforcement Bulletin
Many new technologies can help law enforcement personnel solve crimes and apprehend offenders. While specialists in these fields must keep abreast of new developments, law enforcement personnel do not have to become experts to take advantage of the innovations or to apply the scientific methods. For example, once, albeit a long time ago, authorities often ignored fingerprint evidence at crime scenes because they either did not understand its value or did not have skilled personnel to process it. As specialists became available, however, law enforcement agencies began collecting the evidence. Today, it would prove a misfeasance for an officer or crime scene technician to ignore fingerprints at the scene of a violent crime.
Blood spatter analysis requires the same expert interpretation as fingerprints. Yet, at crime scenes today, authorities often treat blood stains the same as their counterparts did fingerprints a century ago: not routinely measuring or properly photographing them. In many trials, the story composed by the blood that could help law enforcement understand more about what happened during a violent attack or prove a defendant's version of the incident improbable or impossible never gets told.
In the future, resident blood spatter analysts may become as common as fingerprint experts in law enforcement agencies; however, the lack of these specialists in no way should preclude obtaining vital blood spatter evidence at crime scenes. Officers or technicians do not have to interpret the blood spatter but only measure it, record their findings, and photograph the stain so experts can analyze it later.
Recording blood spatter evidence requires little training. Officers and technicians do not have to learn the trigonometric formulas and calculations involved in interpretation. Measurement training does not require weeks of classroom lectures and months of on-the-job experience. Instead, law enforcement personnel can learn the measurement and photography procedures in 2 days at police academy classes, college criminal justice courses, or in-service seminars.
How much knowledge do officers and crime scene technicians need to preserve blood spatter evidence? First and foremost, they must recognize the importance of the evidence--equal to that of fingerprints, shell casings, bullet holes, or murder weapons. Next, they need to understand that blood spatter indicates the direction from which it came. Then, they must learn how to measure the length and width of a single blood drop, how to tell the direction of travel (visible with the naked eye), and how to find the distance from the drop to the point from which the blood came (also visible with the naked eye). Finally, they need to record those measurements. A form with columns can create a permanent record of the blood spatter evidence at a crime scene. These measurements and the photographs are all an expert requires to analyze the evidence at a later time.
A basic understanding of blood spatter analysis allows the first responding officer, crime scene technician, or detective to assist in correctly collecting and preserving blood stain data at the scene. The principles and procedures are not complicated. The interpretation of blood spatter patterns at crime scenes may reveal critically important information, such as the positions of the victim, assailant, and objects at the scene; the type of weapon used to cause the spatter; the minimum number of blows, shots, or stabs that occurred; and the movement and direction of the victim and assailant after bloodshed began. It also may support or contradict statements given by witnesses. (1) The analyst may use blood spatter interpretation to determine what events occurred; when and in what sequence they occurred; who was or was not present; and what did not occur. (2)
Officers or crime technicians can record the measurements of the stains needed and leave it to the experts to interpret them. …