The gunshot residue is important, because if a man/woman has recently shot a firearm, to hurt someone, the gun as soon as it is fired it will leave the residue. So if someone was to commit a crime of any sort using a gun, and they have fired it the scientist can take a swab of the suspects hands, and find out if they are responsible for the crime. The bad part about this evidence is that it is easily taken care of. The suspect could have worn gloves, and gotten rid of them. Therefore there would be no residue on his/her hands.