I don't really care if he is crazy or not. There is not even a trail needed. He admitted his haynes crime, plus witnesses and evidence is in abundance.
He should be hanged by his testicles in the middle of main city square, and let the crows eat his body. And I would hope that maybe, such disgraceful death would be enough of deterrence for other wanna-be killers.
If I was a policeman arresting him, he would be already shot dead "for trying to escape". If not very right, I would at least save taxpayers millions of dollars in his prosecution and imprisonment.
In prison or institute, he is going to write a book and make millions, on other psychopaths and stupid buying it. In mean time he is going to enjoy googling and blogging on free internet, plus standard social privileges and rights of prisoners.
After 20 years he will get out of prison rich, and will enjoy good 30-50 years of the rest of his life, and will be granted another chance to do mass killing of children of Norway.
PS. I'm not sure who is more mentally sick, him or our modern justice system?