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Gunshot Residue and Distance Determination (Distance Determination…
Gunshot Residue and Distance Determination
Powders and Residue - The pattern that results from firing a firearm can indicate the distance at which it was fired from. Residues may be made up of primers, burned powder, residues that are made during the burning of a propellant etc.
Examination
Visual and Microscopic Examination - Involves the use of a microscope to get a more detailed visualization of the piece of evidence
Chemical Testing - Sometime, the residue that is deposited on the target is not visible to the naked eye and need additional chemicals. A few tests that can be done include the Griess Test, the Dithiooxamide Test, and the Sodium Rhodizonate Test
Examination Documentation - typically involves photography and/or drawings/written descriptions
Distance Determination
Residues Consistent with the discharge of a Firearm - Depending on how close the firearm was fired from the target, residues may be deposited onto the target. These residues may be detected via different chemicals
Interpretation Challenges - Depending on how degraded the piece of evidence is, the amount of nitrite may become harder to detect. Some of the tests may also detect nitrite regardless of whether or not it came from a gunshot
Vaporous Lead Residues - This type of residue is deposited with close range and can be detected with the Sodium Rhodizonate Test
Reproduction of Results - The same firearm must be used to determine if the firing patterns are consistent with each other as well as the evidence piece
Nitrite Residues - The closer the muzzle is to the target, the greater the amount of Nitrite that is deposited onto the target
Nitrite Residue Patterns - A firearm needs to be shot at difference distances to determine the types of patterns that result from those distances
Contact Shot - Typically, when a firearm is fired at a very close range to the target, the residues that are discharged will be deposited on the target and cause extensive damage
Shot Patterning - With firearms that shoot multiple pellets, the pattern reconstruction needs to be done with the original firearm and ammunition. The distances in which patterns are achieved is greater than that or regular firearms
Significance of Results - The data/results that are collected should be consistent each time
Chemical Testing - Some of the tests performed to detect residues from gunshots include the Modified Griess Test and the Sodium Rhodizonate Test
Shot Pattern Reproduction - Involves shooting the same firearm at different distances to determine the types of patterns that are created on the target.
Residues Consistent with the Passage of a Bullet - If a bullet passes through an article of clothing or any item, it will leave lead or copper residues that can be detected via the Dithiooxamide Test and the Sodium Rhodizonate Test
Dillon, H. John. “Module 12 :: Gunshot Residue and Distance Determination” Firearm Examiner Training, projects.nfstc.org/firearms/.