The correct answer to this open question is the following.
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The likelihood of detecting gunshot residues on swabs taken from living subjects up to six hours after firing has occurred is less than the likelihood of detecting gunshot residues within two hours of the firing.
Gunshots residue can last six hours after the shooting of the weapon. The GSR stays on the hands of the shooter because it deposits the particles there an on the clothes. This is why police can investigate a suspect, testing the residuals of these particles on its hands or clothes to find if indeed shoot a gun.
