Comparative Evidence Unit:

Distance Determination and Gunshot Residue

There are many instances where it may be pertinent to a case to determine how near or far a firearm was discharged from an object. In a scenario where someone states that they shot another person out of self-defense, knowing the distance that the firearm was discharged would be an example of how this information could either contradict or corroborate a suspect’s statement. This information may also be beneficial when reconstructing a crime scene by determining where a shooter may have been standing when a firearm was being used.

This technique of analysis is known as Distance Determination. When conducting a distance determination, a criminalist is looking at the components that leave the barrel of a firearm when a cartridge is fired. Most think of the bullet being the only thing that leaves the barrel, but there is also a variety of metals, chemicals, and physical evidence in the gunshot residue leaving the barrel that can hit a target as well. The primary components evaluated from the gunshot residue are lead particles, partially burned and unburned gun powder particles, soot, and nitrite patterns. By evaluating these patterns left on the target and comparing them to test patterns made by the firearm and ammunition used in the incident, a criminalist can effectively determine the range that the shot was fired.

In instances where multiple projectiles hit a target from a single shot, as with many shotguns, the physical shot pattern can be evaluated for the purposes of distance determination. Similar to chemical testing, a series of tests using the same shotgun and shotshells would be used to compare to the evidence.

While Distance Determination testing is most commonly performed on the clothing of a victim, a variety of different materials and surfaces (including other cloth materials like curtains or bedding, walls, and sides of vehicles) may also be submitted for evaluation.