I've previously posted about this case. Five judges are set to determine his fate. They must analyze the evidence and motivation behind the killing of 77 people. Breivik claimed that he was acting to protect Norwegian culture from Muslim immigrants. If he is found legally sane and guilty, then he can face up to 21 years in jail.
I suspect this is why the prosecution is asking he be declared legally insane. If he is declared insane, he can spend the rest of his life in mental hospitals. Therefore, he would never get out and be a danger to society again.
If he's found sane and goes to jail for 21 years, he'll get out someday. The defense is asking for this. Even if that day is two decades away, Breivik is clearly dangerous and remorseless. It's an extremely interesting strategy by each side that you may never see in the U.S.
Take New York State for example. We'll assume that the Breivik committed these crimes here. And we'll assume the federal government isn't prosecuting it (although they would in a minute), but the district attorney's office is.
The first step in an insanity case is to test competency. At any time, the judge or either party can have the defendant tested to determine if he's competent to stand trial. Psychiatrists analyze the defendant to determine if he is able to understand the proceedings against him and assist in his defense. This is a low standard. If the defendant knows the job of a judge, the prosecutor, the jury, and his attorney, then he is usually declared fit.
If he's found fit to proceed, then it's on to the next step. The defense attorney, not the prosecutor, interposes the insanity defense. It's found in New York Penal Law Section 40.15. It is an affirmative defense, which means the defendant must prove that he lacked the capacity to know or appreciate either: 1) the nature and consequences of such conduct, or 2) that such conduct was wrong.
This allows a defendant to know what he had done, but still be found not guilty by reason of mental disease or defect because he did not appreciate the legal and moral consequences of the act. It is a very difficult standard to apply, and extremely imposing for twelve average men and women pulled from the street and asked to sit on a jury.
If Breivik was in New York, he would be subjected to 77 consecutive life sentences without parole if convicted. He would serve these sentences with the worst offenders in maximum security prisons. If found insane, he would not be found guilty. Instead he would be confined to a mental institution for a significant length of time.
If Breivik was under the U.S. legal system, he would most likely pursue the insanity defense. It's interesting how one's claim of insanity could change depending on the rules of the game.