OSLO - Prosecutors asked a Norwegian court on Thursday to declare far- right mass murderer Anders Behring Breivik insane and commit him to a mental institution.While not certain that Breivik was not responsible for his actions, they chose to give him the benefit of the doubt in the face of conflicting psychiatric reports, and so to go against the view of most Norwegians that he should go to prison."In our opinion, it's worse to send a psychotic person to preventive detention than to send a non-psychotic person to mandatory care," prosecutor Svein Holden told the court."We are not convinced that Anders Behring Breivik is legally insane, but we are in doubt. So our petition is for a judgment that he shall be transferred to compulsory mental health care."Three out of four Norwegians consider Breivik sane enough for a jail term, according to a poll carried out for the public broadcaster NRK. A pre-trial psychiatric report that found him to be insane created such an outcry that the court ordered another one, which came to the opposite conclusion.Breivik admits to killing 77 people in twin attacks last July, most of them teenagers at a Labour Party summer camp.He says he should be declared sane, but acquitted on grounds that he was defending the Norwegian people by fighting the supporters of Muslim immigration.If the court finds him to have been insane, he has said that it will be "worse than death", and he will appeal.Most Norwegians, too, find it hard to understand how someone could be insane and yet spend years planning such a spectacular attack so meticulously.Breivik first detonated a bomb outside government headquarters in Oslo to create a diversion, then systematically gunned down 69 people, mostly teenagers, at a summer camp run by the ruling Labour Party on the island of Utoeya."What is most incomprehensible is how unaffected he was by his acts," prosecutor Inga Bejer Engh said."He described without remorse or feeling how these young people begged for their lives, and how he shot them in the head to make sure they were dead."The trial ends with closing defense arguments on Friday. The two professional and three lay judges are due to reach a verdict by Aug. 24.