[quote name='h3llbring3r']If you truly fear for your life how does that change the equation?
Mentally deranged people kill sane people all the time; like pushing them in front of a subway train, or bleeding their demons out.[/QUOTE]
This.
The issue here is the perceived threat on one's life. Regardless of the mental capacity of the criminal in question, if the student feared for his life (and who's to say he didn't? How would any of us react to a strange person in our home who is clearly there with bad intentions?), all bets are off. If the criminal had some kind of history of mental illness, or even an adult-child disability, then you could maybe make a case. But even so, the person he's trying to rob isn't aware of that. In that instance, I think it just becomes an unfortunate accident. It's hard to say how threatened a person should feel with an intruder in his home.
The fact of the matter is, the history of the criminal alone should be enough to protect the student from any charges. It's not like some mentally handicapped teenager with no criminal record just wandered into the guy's garage, and he freaked out and chopped him to bits with his katana. The burglar made a conscious decision to break the law and steal from this guy, and he got more than he bargained for. To sum up: too bad, so sad. The last thing we need to be worrying about are the rights of people who completely disregard the rights of everyone else.