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Gunshot residue results from the discharge of a firearm. This includes primer, powder, and/or projectile material and products of their combustion. The residue that can be deposited on the hands of a shooter is usually the result of gases or particles escaping through openings in the weapon (such as the cylinder area of a revolver) or leaving the end of a barrel. The actual amount of residue on the hands varies with the type of weapon, ammunition, and conditions of discharge.
The analysis of gunshot residue from the hands of a shooter detects primarily trace amounts of primer residue. Gunshot residue (GSR) deposits on the hands decline rapidly during the first hour after firing the weapon. In practice, GSR cannot be expected after six hours from a living subject. However in suicides, GSR can last many hours after the time of shooting. In either case, correct sample collection techniques are critical. Sampling for GSR should be performed on a live subject as soon as possible after the shooting. Ideally, samples should be taken immediately after contact with a subject in the field. A single collection kit providing for Scanning Electron Microscope (SEM) adhesive disc type sampling collection methods should be used.
Caution! The subject should not be allowed to wash or rub his/her hands prior to sampling. The subject should not be fingerprinted prior to sampling. Prior to any residue collection from the hands, visually examine the subject's hands and wrists. Record the position of any visible gunshot residue deposits (black smudges) or particles with a photo or sketch. Avoid contact with the subject's hand since this may contaminate them. Also avoid cuffing the subject's hands behind his back, if possible, since this will tend to remove any GSR from the back of the hands.
Caution! Do not touch the hands of the subject in the areas to be sampled for possible gunshot residues.
If possible, thoroughly wash your hands and wrists before proceeding further to prevent any transfer contamination to the hands of the subject. Put on disposable plastic gloves provided before handling any sampling materials. Be sure to follow the instructions carefully. Support the hand to be sampled by holding the arm above the wrist. Have the subject relax and flex the hand during collection to allow the adhesive access over the wrinkled areas around the knuckles and palm. Do not peel off or touch the sticky surface. Do not include gloves with the samples.
Instructions for Collecting, Packaging and Submission of Gunshot Residue (GSR) from Persons Suspected of Discharging a Firearm using adhesive coated discs for SEM analysis.