It shouldn't.
I don't know what the NGRI laws are in Norway. They could be more lenient vs. the U.S. In the U.S., in most states, iwe follow the M'Naughten rule meaning that in general, the NGRI standard is someone has to be of a mental state where due to a "mental disease or defect" they did not know the difference between right vs. wrong during the exact moment they commited the act.
Some easy examples of an NGRI: schizophrenic guy holds a what he believes to be a tree branch (that in reality is a gun) and shoots someone, killing them; guy kills someone sincerely believing that person is Satan (due to mental illness) and that he's saving the human race by killing the victim.
Some easy examples of something that is not NGRI: Person has pathological gambling and robs a bank to fund his gamling problem, someone is depressed and decides to get it on with a hooker as a form of "therapy" to ease his depression.
In some states, there is no NGRI allowed. They got fed up with malingerers getting good press and getting an NGRI through the court so the state legislature actually got rid of it. In these states it's called guilty but mentally ill. Despite this phenomenon, it's actually rare for someone to get a successful NGRI plea and the public perception that this is common is more the result of such cases getting a lot of press. (Kinda like a jackpot ringing. Most people are losers, but the one winner's machine bells and whistles through the roof).
In one state, they actually have a legal standard that so long as the crime was somehow connected to a mental illness, you can use an NGRI plea. So in this state, someone robbing a bank to fund his gambling problem, well you could actually use an NGRI defense, and the law is supposed to give it to you. (Yeah I know, crazy, but that state still hasn't changed their laws on it. As one of my forensic psychiatry profs said, if you want to rob a bank, go there).
My personal opinion, only based on what we see in the news, and I believe this is still within professional guidelines because I'm not giving a real conclusion: there certainly were things about him begging the question that he was schizophrenic (or had some other type of psychosis) but they were also within the realm of having extreme political beliefs that were not due to mental illness. I would've had to investigate the case more to come to a conclusion.
Reason why I say this, and most of you might not be aware of this not having lived in Europe, is there is an emerging faction of people that are extremely Islamophobic. They are in several people's minds a 21C equivalent of the Nazi movement. While we don't see this in the U.S. news, if you read European news all the time, here and there you see occasional mentions of this movement. It's small enough for most Americans to overlook it.
He suffers "grandiose delusions" and "believes he is chosen to decide who is to live and who is to die,"
That in and of itself is not grounds to say someone is "insane" under the M'Naghten standard. Several Nazis from WWII had this belief with regards to Jews. Several rapists believe they have the right justified by force to rape others. A Klansman would've had that view of an African American during a lynching.
That is not to say the Norway ruling was wrong in a legal sense. I don't know their legal standards, and their mental health experts that investigated this case may have had knowledge I didn't know about that was significant in their decision making process.
