Why do you think it might be stolen? Weren't you leery before if you feel that way now? Ask yourself, is this guy a GOOD friend or just someone I know? Also, do any serial numbers look to be tampered with. I'd first go back to the guy and tell him I want my money back. If he refuses, I'd go to the police and tell him everything I knew about the guy, address, phone etc. Show them the gun. Maybe everything is fine, maybe not. You sure don't want to get caught holding a stolen gun of any kind. You may end up losing your gun and money, but it's better than losing your freedom. If you do lose either the gun or money, [it may be hard to take] chalk it up to experience learned and be glad you won't have to keep looking over your shoulder.