what will be the next move?

Ok, my friend is an idiot let's get that out the way first and foremost. He has a gun, he got it from some friend. No it isn't registered or anything, he just keeps it for protection. He's an older guy, not a young street thug or anything, regular working guy. Today he went out and as usual put the gun on the trunk of the car while he opened it and did little crap before he got in. He forgot it on the trunk,drove all the way to the mall and when he came out of course cops had surrounded his car. He told them he didn't know where it came from. They took all of his info and asked him a few questions and let him go. He's been sitting at home scared as hell at what might happen next. He keeps saying they're gonna come and take him to jail, he's gonna lose his job etc. I am tired of him asking me what I think will happen, because I don't know. What will probably be the next move on the part of the police?