If you read all the stories, you will see that he went a tad far and so will probably go away for a long time.
He heard the first person coming down the stairs and shot him through the body. Then shot him again in the head at close range. The girl was coming down the stairs a short time later and he shot her as soon as he could see her hips. When he went to shoot her again, the rifle jammed. So he took out a pistol and shot her in the head from close range.
If that is a correct account of what happened I think he is in big trouble.
This is from his statements.
If he did those things he forfeits any sort of benefit of the doubt. His best bet is temporary insanity in that case.