A psychiatric evaluation of mass murderer Anders Behring Breivik found he was insane when he killed 77 people in a Norway rampage on July 22.

Oslo prosecutors argued on Tuesday that Breivik - a self-styled anti-Muslim resistance fighter - should be sent to a psychiatric ward instead of prison saying he was psychotic at the time of the worst peacetime massacre in Norway's history.

"The conclusions of the forensic experts is that Anders Behring Breivik was insane," prosecutor Svein Holden said.

In their report, the experts describe a man "who finds himself in his own delusional universe, where all his thoughts and acts are governed by these delusions," Holden said. "They conclude that Anders Behring Breivik during a long period of time has developed the mental disorder of paranoid schizophrenia, which has changed him and made him into the person he is today."

Ordinarily, a psychotic person cannot plan and perform even simple tasks - such as driving a car - which runs counter to the meticulous execution of Breivik's carefully planned killing spree. There are, however, exceptions.

The 243-page report produced by two psychiatrists who spent a total of 36 hours interviewing Breivik will be reviewed by a panel from the Norwegian Board of Forensic Medicine before the courts issue a ruling. The board will be tasked with determining if the report's conclusions conform to the legal definition of insanity.

According to legal experts, an insanity defense in Norway requires the defendant be in a state of psychosis while committing the crime with which he or she is charged. That means the defendant is so disassociated from reality they are no responsible for their actions.

"Breivik has confessed to carrying out the attacks but denies criminal guilt, saying he's a commander of a Norwegian resistance movement opposed to multiculturalism.

Investigators have found no sign of such a movement and say Breivik most likely plotted and carried out the attacks on his own.