Forensic Science of Bloodstain Pattern Analysis
Process of Evaluating Blood Spatter Evidence at a Crime Scene
Nov 15, 2009
Showtime's quirky hit drama Dexter profiles a serial killer who works as a bloodstain pattern analyst for the Miami-Dade Police Department. The character is fictional, but the forensic analysis is real. First, the presumptive bloodstain must be analyzed to ensure it is human. Then the analysis of the blood spatter patterns begins.
Blood Spatter Analysis is a Forensic Science
During a violent crime like a homicide or assault, blood spatter is dispersed across many surfaces in a crime scene. Analysis of these stains and the pattern they create can tell the forensic technician many things about how the crime occurred. According to Michael Dickerson's Studies in Bloodstain Pattern Analysis website, blood spatter evidence can reveal:
- the victim or accused's movement and position at the time of the incident
- where the blood originated
- number of times the victim was injured
- possible weapon used in commission of the crime
- time when the crime may have occurred.
Passive Bloodstains
Passive bloodstains occur when blood drips from a wound or object. Blood dripping into a sink when someone cuts their finger while cooking is an example of a passive bloodstain. Passive stains are further characterized by the presence of
- drops
- drips
- clots
- pools of blood.
The flow of passive bloodstains is also analyzed to help determine volume. Passive bloodstains are considered to be low velocity bloodstains. Low velocity bloodstains generally leave large blood drops.
Transfer Bloodstains
Transfer stains occur when a bloody object comes into contact with another object. Bloodstain analyst, Joseph Slemko, reports in his Bloodstain Pattern Analysis Tutorial (online), transfer stains can be divided into contact patterns, swipes, wipes, and smudges.
A contact pattern may be a bloody hand or shoeprint that can be further analyzed for fingerprint data or shoe identification. A swipe occurs when a bloody object contacts an object without blood, while a wipe is the opposite.
Projected Bloodstains
Blood is projected when some type of force is applied to it. These types of stains include
- arterial spurting
- cast-off stains
- impact splatter.
Arterial spurting is just what it seems, blood spurting or gushing from a severed artery after an injury. Cast-off stains come from a bloody object in motion, such as a knife moving back and forth in a stabbing. Impact splatter happens when a object containing blood is hit with some type of force. A blow with a blunt object may result in a low or medium velocity spatter stain while a gunshot pattern is generally considered to be a high velocity stain. A high velocity spatter stain will have very small blood drops.
Crime Scene Bloodstain Analysis
Bloodstain pattern analysis reveals much information during a crime scene investigation. Clues to the weapon used in the incident are developed by analyzing the type and velocity of the stain. Further information can be found by calculating the direction and angles of impact of the blood spatter evidence.
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