I'm going to go against the grain here, but has he done anything to suggest that he might be violent? Just because he has some mental health issues doesn't mean he's violent and it seems like stigmatizing him to suggest that he is without some indication that he might become violent or threatening. If you think it's an issue though, maybe talk to campus security and see what they suggest. Maybe they can run a background check on him or something. It's really unfortunate that he's not making use of the help and resources that are being offered to him.