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Gunshot Residue Testing
Transcript of Gunshot Residue Testing
Those where a pattern of residues is found on the evidence garment and the questioned firearm and ammunition are recovered
Those where a pattern of residues is found on the evidence garment and the firearm and ammunition are not recovered
Those where only trace amounts or no residues are found on the evidence garment Modified Griess Test The first test conducted because it doesn't interfere with later tests for lead residues
Its a test to detect the presence of nitrite residues (Byproduct of combustion of smokeless gunpowder. Nitrite particles are expelled when a firearm is discharged from the muzzle& can be imbedded in or deposited on surface of target)
Modified Griess Test is the most commonly used test used by firearm examiners to determine the muzzle-garment distance Composition of Gunshot Residue Can consist of both burned and unburned primer or powder components, and can be used to detect a fired cartridge.
Gunshot residue may be found on the skin or clothing of the person who fired the gun, on an entrance wound of a victim, or on other target materials at the scene. The discharge of a firearm, particularly a revolver, can deposit residues even to persons at close proximity (interpretations as to who fired the weapon should be made with caution)
Sodium Rhodizonate Test Is a chemical test designed to determine if lead
residues are present
Its performed by spraying the exhibit with a weak
solution of Sodium Rhodizonate & distilled water
The solution has a dark yellow/ orange color The major methods for detection of primer residues are analytical and qualitative.
Analytical methods include atomic absorption spectrophotometry (AAS) and inductively coupled plasma mass spectroscopy (ICP-MS).
Scanning electron microscopy with energy dispersive analysis (SEM-EDA) and atomic force microscopy (AFM) are used to identify the primer residue qualitatively.
For these methods, samples must be obtained from the skin surfaces of a victim at the scene. Delay in obtaining residues, movement, or washing of the body prior to autopsy will diminish or destroy gunshot residues Detection of Gunshot Residue http://www.firearmsid.com/a_distanceresults.htm http://library.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNGSR.html The exhibit is placed face down against a piece of treated photo paper and the bullet hole centered on the paper The back of the exhibit being examined is steam ironed with a dilute acetic acid solution in the iron The acetic acid vapors penetrate the exhibit & a reaction takes place between any nitrite residues on the exhibit and the chemicals contained in the photographic paper-The reaction will appear as orange specks on the piece photographic paper. The exhibit is then sprayed with a buffer solution which causes the background color to disappear. The Sodium Rhodizionate reacts with any lead that may be present and turns the lead a very bright pink. The pink color is only an indication of the presence of lead residue and to confirm the presence of lead residue the area can be treated with a diluted Hydrochloric Acid solution. The major primer elements are:
lead (Pb), barium (Ba), or antimony (Sb)-Usually, all three are present
Less common elements:
aluminum (Al), sulfur (S), tin (Sn), calcium (Ca), potassium (K), chlorine (Cl), copper (Cu), strontium (Sr), zinc (Zn), titanium (Ti), or silicon (Si).
A mercury-fulminant based primer may be found in ammunition manufactured in Eastern Europe and used in the Middle East
Primer elements may be easier to detect in residues because they do not get as hot as the powder.
"Lead free" ammunition may contain one or more elements including:
strontium (Sr), zinc (Zn), titanium (Ti), copper (Cu), antimony (Sb), aluminum (Al), or potassium (K).
Elements of Gunshot Residue http://www.youtube.com/watch?v=XQXykgqluyw Clarissa Castaneda