Module 12: Gunshot Residue and Distance Determination
Powders and Residues
bullet propellants and other gunshot residues are expelled from the muzzle during the firing process
gunshot residues are composed of the following
primer residues from the combustion of the cartridge priming mixture when the primer was struck by the firing pin
residues resulting from the burning of the propellant
material generated by the interaction of the bullet with the inside of the barrel
unburned and partially burned powder
Examination
when a firearm is discharged and the bullet strikes a surface, gunshot residues are deposited
some residues are visible and others require chemical treatment in order to visualize them
examination documentation
visual, microscopic, and chemical examinations should be documented according to laboratory protocol
written documentation can be supplemented with images of items indicating the presence of items indicating the presence of physical effects and gunshot residue
visual and microscopic examination
preliminary visual and microscopic examinations of gunshot residues should be given first priority because subsequent chemical testing can dislodge residues or alter the appearance of physical effects
Chemical Testing
Modified Griess Test
for nitrite compounds, a product of burning a nitrate, such as smokeless powder, or Reverse Modified Griess Test
Dithiooxamide Test (rubeanic acid test)
for cuprous (copper-bearing) materials
Sodium Rhodizonate Test
for all forms of lead residues or Bashinski Transfer Technique
test procedure
1. confirm nitride sensitivity of test paper
2. mark reference points of evidence on test paper
3. create layers of reaction items
4. heat reaction layers
5. examine and interpret the results
test procedure
1. confirm performance of all preliminary examination and tests
2. place a test marker on the item to be tested
3. position the area to be tested
4. perform the color test
5. examine and intepret results
6. dry test item
1. confirm performance of all preliminary examination and tests
2. place a test mark on the item to be tested
3. position the area to be tested
4. perform the color test
Interpretation
residues consistent with the passage of a bullet
residues consistent with the discharge of a firearm
challenges
holes found in objects, such as garments, with no accompanying particulate residues
positive results for the presence of any copper-bearing or lead-bearing residues from either or both of the Dithioxamide Test and the Sodium Rhodizonate Test
will result in the deposit of particulate lead around a bullet hole
may be in the form of tiny solidified droplets resulting form the surface erosion of a bullet during its passage through the barrel
rough handling, wet weather conditions, large amounts of dried blood, extended exposure of a body to the outdoors, large amounts of unburned ball powder