Prosecutors said on Thursday that Anders Behring Breivik, who killed 77 people in Norway last July, may never be free again if the court follows their request and sends him to a closed psychiatric ward.

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"There has been a lot of speculation during this case that being sentenced to psychiatric treatment would mean he could get out tomorrow," prosecutor Inga Bejer Engh told reporters after the second last day of trial.

"We do not live in such a world... It is obvious that there are criminals who have been sentenced to psychiatric treatment and who get out relatively quickly, but there are also killers sentenced to a closed care unit and who probably will never get out," she added.

Bejer Engh's remarks came after she and her colleague Svein Holden wrapped up their closing arguments, insisting Breivik's sanity had not been proven beyond a reasonable doubt and calling for the court to send the 33-year-old confessed killer to a closed mental ward instead of prison.

"Our request is that he be obliged to undergo psychiatric treatment" in a closed unit, Holden said.

He added though that if the Oslo district court's five judges instead opted to find Breivik criminally sane, they should sentence him to Norway's harshest penalty: 21 years in prison with a provision that allows the sentence to be extended for as long as he is considered a danger to society.

Breivik, who is intent on being found sane to ensure his Islamophobic ideology is not written off as the ravings of a lunatic, was visibly annoyed by the prosecution's call for psychiatric treatment.

Following Holden's remarks, the 33-year-old right-wing extremist stood up and touched a clenched right fist to his chest before stretching his arm out in a nationalist salute he had made on the first days of his trial in April but had stopped doing at the request of his lawyers.

After the proceedings, Bejer Engh meanwhile stressed that Breivik's crimes were in a league of their own and that he could not be compared to criminals currently locked up in psychiatric institutions.

"We have here a man who throughout the entire 10 weeks of the trial has remained totally indifferent to his actions. It is obvious that (showing remorse) is something that is completely decisive in determining whether or not he remains a danger to society," she said.

On July 22nd, 2011, the right-wing extremist first bombed a government building in Oslo, killing eight people, before going on a shooting rampage on the nearby island of Utøya where the ruling Labour Party's youth wing was hosting a summer camp.

He killed 69 more people on the island, most of them teens, with the youngest having just celebrated her 14th birthday.