Contrary to reports of some sort of inversion it is not the case that shell cases need to be found at the scene of a crime to cause an arrest and conviction. There are many people who are serving time after having left their fingerprints on shell cases found in a gun recovered after a crime. If the gun can be linked to a crime scene via balistics reports and the shells in the gun to an individual via fingerprints that is circumstansial evidence. Of course nobody gets sent to jail on a single piece of questionable evidence (at least if they have a decent lawyer). But a weak piece of evidence is sufficient to lead to a conviction if it is a lead. Anything that reduces the search space for an investigating team is an advantage for the police. Phill