The success or failure of any criminal investigation often depends on the recognition of physical evidence left at a crime scene and the proper analysis of that evidence.
Crime scenes that involve bloodshed often contain a wealth of information in the form of bloodstains. The pattern, size, shape, and the location of such stains may be very useful in the reconstruction of the events that occurred.
William G. ECKERT and Stuart H. JAMES
Bloodstain Pattern Analysis:
The examination of the shapes, locations and distribution patterns of bloodstains in order to provide an interpretation of the physical events by which they were created that is based on the premise that all bloodstains and bloodstain patterns are characteristic of the forces that have created them.
The interpretation of bloodstain patterns found at the scene or on exhibits such as the clothing of the principles of the occurrence can be used to:
Confirm or refute assumption concerning events and their sequence:
Postion of victim (standing, sitting, laying)
Evidence of movement (blood smears, flow patterns and drip trails)
Confirm or refute statements made by the principles in the case:
Are the stain patterns on a suspect's clothing consistent with his reported action?
Are the stain patterns on a victim and/or at the scene consistent with accounts given by the witnesses, victim or the suspect?
Properties of Blood:
On average accounts for 8% of total body weight
5 to 6 liters of blood for males
4 to 5 liters of blood for females
A 40% blood volume loss, internally and/or externally is required to produce irreversible shock (death)
A blood loss of 1.5 liters internally/externally is required to cause incapacitation.
Surface Tension in Blood:
The elastic like property of the surface of the liquid caused by the forces of attraction between the molecules of the liquid that makes it contract and assume the smallest possible shape i.e. a blood droplet in flight will possess the shape of a sphere (ball).
Target Surface Texture:
Bloodstains can occur on a variety of surfaces such as carpet wood, tile wallpaper, clothing and the list goes on........
The type of surface that a blood droplet strikes affects the amount of resultant stain distortion and satellite (secondary) blood spatter.
Blood droplets that strike a hard smooth surface, like glass, will have little or no distortion on their peripheral edges.
Blood droplets that stirke linoleum flooring will take-on a slightly different appearance and may tend to have "scalloping" on their peripheral edge.
Surfaces such as wood or concrete will be distorted to a much greater extent, sometimes producing satellite (secondary) blood spatter droplets and stains.
General Categories of Bloodstains:
(caused by the force of gravity only)
(a blood contaminated object(s) contacting a surface)
Spatter Patterns (impact, cast-off, etc.)
(liquid blood, internally or externally, subjected to a force greater than gravity)
A transfer bloodstain or bloodstain patterns is created when a wet, bloody surface contacts another surface.
A recognizable image of all or a portion of the original surface may be observed in the pattern.
Transfer bloodstain can be further subdivided into: contact bleeding, swipes or wipes.
Drip Stains and Patterns:
Created or formed by the force of gravity acting upon liquid blood.
This category also includes drip trails and flow patterns.