Mental illness as an autistic child.

This is out of left field, and maybe not helpful in any way, but you might consider a brain biopsy to see if he has some kind of brain infection.
I'm not suggesting that has anything to do with the autism, but certain brain infections can cause behaviour that is considered psychotic, and they are treatable. It might be a complete waste of time, but I'd look into it.

Our oldest is autistic, but very high functioning. We have been blessed with help throughout his life, though there were many times we had to fight the school system for what he needed.
Early diagnosis, some good doctors, ABA and other therapies, social story boards and other strategies helped moderate his problems and have kept high functioning. While there were many struggles along the way, we've been blessed that he has never gone to some of the terrible extremes many have experienced. He's 24 now, and we don't know if he'll ever be able to live on his own, but he is relatively self-sufficient. He still isn't very good in social situations, but he's much better than he was when he was younger about blurting out inappropriate, insensitive, or otherwise embarrassing statements.

Praying that you find competent doctors who can help him, and are willing to take the time to do so.