Yes and no. It could go either way. Someone mentioned it earlier (in this thread I beleive, but I read a lot of threads tonight on guard duty), but the possible destruction of evidence COULD be grounds for a warrantless seizure. However, once the person who is in possession of the evidence is detained, a warrant would probably be sought and issued. It is nearly impossible however, to gather the evidence if the unknown person in possession of it disappears into the chaos of a shooting scene.