OSLO (AFP) - Anders Behring Breivik, who killed 77 people in twin attacks in Norway last July, may never go to jail after psychiatrists ruled him criminally insane, prosecutors said Tuesday. Instead, the 32-year-old gunman could spend the rest of his life in a mental institution, prosecutor Inga Bejer Engh told reporters in Oslo. The prosecutor was speaking after forensic experts submitted a psychiatric evaluation Tuesday in which they found the gunman insane. "If the final conclusion is that Breivik is insane, we will request that the court in the upcoming legal proceedings pass sentence by which Breivik is subjected to compulsory mental health care," Bejer Engh said. The 243-page psychiatric report, which must still be reviewed by a committee of forensic experts, found that Behring Breivik had developed paranoid schizophrenia over time. The two experts who conducted 13 interviews over 36 hours with the right-wing extremist described a person in his own "delusional universe," said another prosecutor, Svein Holden. Holden said the report concluded that Behring Breivik had "grandiose illusions whereby he believes he is to determine who is to live and who is to die." On July 22, he first set off a car bomb outside government buildings in Oslo, killing eight people. After that, he went to the island of Utoeya, some 40 kilometres (25 miles) northwest of Oslo, where, disguised as a police officer, he spent nearly an hour and a half methodically shooting and killing another 69 people attending a summer camp, most of them teenagers. Although he has confessed to the facts, Behring Breivik has refused to plead guilty, claiming he was waging a war and that his actions were "atrocious but necessary." He has previously said he was on a crusade against multi-culturalism and the "Muslim invasion" of Europe. He "committed these executions out of love for his people as he describes it," Holden said. In his talks with the experts, Behring Breivik predicted a scenario whereby "his organisation, the Knights Templar, take over power in Europe and he puts himself forward tentatively as the future regent in Norway." The trial is scheduled to open on April 16, 2012, and last for about 10 weeks. The Oslo court will have the final say on whether Behring Breivik can be held legally responsible for the crimes, though it generally follows the experts' recommendations. If he is declared criminally insane and sentenced to closed psychiatric care, a judge will review his sentence every three years. If he recovers from his illness, he could theoretically be transferred to a prison if he were considered a threat to society. He could also be released if the opposite scenario were to present itself. The killings were the deadliest attacks committed in Norway in living memory, and profoundly shocked the normally tranquil nation.