Why?  If the knife that you lost in the woods shows up at a crime scene, does that imply that you are the criminal?  If a gun shows up at a crime scene, the same procedures used for any other evidence applies.  The gun is not the problem, the identification of the criminal is the issue not the "things" that the criminal brought with them.  If the criminal killed with a baseball bat but had a gun with him, is it the gun's fault?  And just for the sake of discussion, bats/clubs, knives or fists/feet kill more people every year than long guns, like AR-15 and AK-47