I feel your pain. My foster daughter just turned 14 and has Asperger's Syndrome as well as a rare condition called RAD (Reactive Attention Disorder). She is also very strong, and impossible to control. She's even beaten up boys that are way bigger than her, and she works out a lot.
She is very violent, and even broke another girls' nose when she was 10, and her nose was even displaced so it doesn't look as it did before.
We've tried getting her individual lessons for boxing, and it has helped her bit. but the problem is it gave her more skills to help her beat up other people.
Now if you really think that Asperger's has something to do with it, you're wrong. He must have something else, because Asperger's doesn't make people THAT violent.
First off jlevin, i think that one of the issues that needs to be further explored is WHY he doesn't want to take his medicine, is it because he thinks he doesnt need it or something? Another thing is the question of what is triggering these violent outbursts? is it stress, someone making a comment about something, etc.
I'm talking from personal experience here by the way. Usually with me the problem usually starts out small, like say my Dad wants me to empty the dishwasher, and I say "no, I don't want to, and nothing's preventing you from doing it" from there the issue would escalate to something like my Dad cutting off the internet, or attempting to take away my laptop. The problems then build on themselves from there.
Asperger's Syndrome alone does not cause these issues. It's more a misunderstanding that's placed there due to the disorder. Basically meaning, that like in the example of my dad asking me to empty the dishwasher, I'll interpret it as him being lazy and trying to delegate all his jobs off to other people (when he really already does quite a lot).
Also in some cases of people with Asperger's, removing them from a familiar area/situation, and putting them into a new unknown place can cause more problems than it solves.
I understand that you want to help their family out jlevin, but it seems that the actual problem is a lot more deep seated than initially thought. There seem to be a couple solutions to this issue. The first issue that needs resolving is that their family needs to regain a sense of security and control again. The parents need to be put back in control of the situation is basically what i'm saying. So now that i've said that...I'm about 50/50 on this solution, basically that the next time an outburst occurs that they need to call the police. Now here's why im debating whether this will help or not. The problem is that since he's over 18, the police can charge him with assault or domestic abuse or both. This most likely would land him in jail, which in my mind would probably only serve to make things worse as he'd probably think it was his family's fault he got sent there. So instead of making things better, it would make things worse. Although there's the chance that it could turn him around for the better, I don't know.
Secondly, I'd say that their family should talk to his psychiatrist ASAP and bring up the issue of the violence, and see what the psychiatrist says and reccomends to be done.
Third, I'd probably say that in order to get to the actual core problem, their family should possibly think about a therapist. Talk therapy can be very helpful as it would most likely be a chance for him to tell his side of the story as well as hear what the other perspective is.
Hope this helps