Go easy on this guy and get all the fact together before shooting him.
The poor sucker may have bought it of the thief and know nothing of it's background.
Then again he could be the dog who stole it.
I once made an arse of myself (actually, I've done it more than once) when someone returned one of our mixers that was stolen out of a venue for service and I nearly called the cops on him. The poor guy had bought it out of a used equipment store who had bought it from someone else.