I’d think his life expectancy would be shorter in a mental hospital than in prison. Those are scary places and it only takes one wacko to get a wild hair and it’s lights out. Imagine the mental fatigue you’d have after living 24/7 in a place like that. It might prove a better punishment if it was guaranteed he’d never be let out.
There have been efforts to adjudicate him as sane, but he must be a good actor or some psychiatrist has been bribed because he's still mooching off the state at that facility.