Here is the update: He came back late at night and found all his stuff outside and the doors locked. He called and threatened to sue us for damaging his things and that he was going to call our landlord and get us kicked out. He then started stammering around and knocked on a neighbor's door, at which point, they called the police. The police talked to us and him for a while, and then told him that he has to pack up his stuff, and he can't stay around here. They told him to go sleep in his car somewhere else.
So things seem to have worked out pretty uneventful and nice so far. I would say that the moral of the story is to be very cautious about who you let stay in your home, and don't give unwelcome guests too much leeway. I was pretty astonished at what the police on the phone told me, and what I found in articles like this:
http://www.sptimes.com/2004/02/17/Ta...n_favor_.shtml
If I had given him a key, let him recieve mail at my place, or even let him stay a few weeks, things probably would have been much more difficult.