Forced placement in a facility for treating mental illness until his doctors determine he is sufficiently well to be reintegrated into society, followed by a public-service program as societal (note: not personal) recompense for his actions. That would be after the first time, though, not the third. Because this person needs help and is plainly not getting it--and he will never get help in an American prison.
But because enough people are more interested in vengeance than justice--and your posts pretty firmly demonstrate that you're in that camp--it will never, ever happen.
I'm not interested in vengeance, and nothing about my post suggested I am. I don't want people who are a danger to society to continue to be a danger to society. If I was one of the people interested in vengeance, I'd have said something like they should get raped repeatedly with a broom in prison. I didn't, I just said they should be locked up. Nothing vengeful about that at all. I just want them to not be near my loved ones.
Putting someone in a concrete box where one's safety is utterly left up to chance is nothing but vengeful and retaliatory. It is designed to inflict misery and nothing else. It saddens me that this obvious fact escapes so many of my fellow Americans but I've become resigned to the fact that those of us with privilege are just kind of shitty human beings when it comes to anybody unlike us.