Odd Andersen / AFP - Getty Images
Self-confessed mass murderer Anders Behring Breivik speaks with a lawyer at a court in Oslo on Friday.
Updated at 11:35 a.m. ET: OSLO -- A Norwegian court ruled Friday that confessed mass killer Anders Behring Breivik was sane, deciding he was criminally responsible for the massacre of 77 people last summer.
Reading the ruling, Judge Wenche Elisabeth Arntzen said that "in a unanimous decision ... the court sentences the defendant to 21 years of preventive detention."
However, such sentences can be extended under Norwegian law as long as an inmate is considered dangerous. Experts have said Breivik is likely to spend the rest of his life behind bars. Norway doesn't have the death penalty.
Prosecutors had demanded a verdict of insanity, a fate Breivik called "worse than death," while many of his victims had said only a sane person could have carried out such a complex attack.
Breivik, 33, detonated a fertilizer bomb outside a government building that included the prime ministerial offices last July, killing eight, then gunned down 69 people, mostly teenagers, at the ruling Labor Party's youth camp on Utoya island.
After the ruling, Breivik told the court he would not appeal the decision.
"He is getting what he deserves," Alexandra Peltre, 18, whom Breivik shot in the thigh on Utoya, told Reuters. "This is karma striking back at him. I do not care if he is insane or not, as long as he gets the punishment that he deserves."
Another survivor of the massacre, Eivind Rindal, told the Norwegian newspaper VG that “it is important that the defendant gets his punishment but the most important thing is that he never gets out.”
“There are many who shared his extreme views in our society,” Rindal added, according to an English translation in the Telegraph newspaper.
Trine Aamodt, whose 19-year-old son was shot at Utoya, told VG she was “happy with the verdict of sanity and am also very glad that there was consensus from all the judges.”
Guilt never a question
Guilt had never been a question in the trial as Breivik described in chilling detail how he hunted down his victims, some as young as 14, with a shot to the body and then one or more bullets to the head.
The killings shook this nation of five million people which had prided itself as a haven from much of the world's troubles, raising questions about the prevalence of far-right views as immigration rises.
Tens of thousands of people gathered in Oslo to sing a children's song calling for peace, as a protest against mass killer Anders Behring Breivik. Msnbc.com's Dara Brown reports.
Few believe anyone would ever sign Breivik's release papers. One of the reasons Breivik's attacks were presented in such gruesome detail during the trial was so that the horror of Oslo and Utoya would be well-documented for the day Breivik asks to be released.
Czech police accuse man of plotting Norway-like copycat terrorist attack
The court’s ruling actually imposed a minimum sentence of 10 years and a maximum of 21.
But Jo Stigen, a law professor at the University of Oslo, told NBCNews.com that Breivik was unlikely to be released for decades.
“This means as long as he is dangerous he will not be free. It’s a potential life sentence … I can hardly see it will be considered he’s not dangerous in 30 or 40 years,” he said, speaking by phone from outside the court.
Odd Andersen / AFP - Getty Images
Labor Party secretary Raymond Johansen, center, hugs a relative of an Utoya massacre victim before Breivik's arrival in court on Friday.
After serving the 10-year minimum sentence, Breivik will be evaluated periodically. Stigen said it was “theoretically possible” he could be released in 10 years, but added this was highly unlikely.
After 21 years, the prosecution can seek to have Breivik kept in prison -- Stigen said that “most certainly they will” – and a court will then decide whether to keep the mass killer in prison.
Norway prison seeks 'friends' to play hockey, chess with mass killer Breivik
The trial and a commission of investigation into the country's worst violence since World War Two have kept Breivik on the front pages for the past 13 months and survivors said the verdict would finally bring some closure.
"It has been a tough year... but I don't want to be Utoya-Nicoline for the rest of my life," said Nicoline Bjerge Schie, a survivor of the shooting, ahead of the verdict.
Friends and family of his victims looked on Friday as Anders Breivik calmly describes chasing down and killing dozens of teenagers during a shooting spree last year on Utoya Island in Norway. Msnbc.com's Al Stirrett reports.
As a result of the ruling that he is sane, Breivik will be locked up in solitary confinement inside the maximum security Ila prison on the outskirts of Oslo. He will return to his relatively spacious cells, enjoying the comforts of a computer, newspapers and a separate exercise room.
Anders Breivik to Norway court: I killed 77 people but am not guilty
One team of court appointed psychiatrists concluded Breivik was psychotic while another came to the opposite conclusion. To make the ruling more difficult, several other experts who testified described a series of mental conditions Breivik suffered from.
Polls showed that around 70 percent of Norwegians thought such a well-planned attack could not have been the work of a madman and Breivik must take responsibility rather than be dismissed as merely deranged.
The nation looks to rally after a bombing and shooting spree leaves 77 people dead.
Breivik himself argued for a verdict of sanity as he wanted the attack to be seen as a political statement rather than an act of lunacy.
He rejected criminal charges out of principle, saying he doesn't recognize the court's authority because it represents a political system that supports multiculturalism -- the reason why he targeted the Labor Party.
NBC News' Ian Johnston, Reuters and The Associated Press contributed to this report.
More world stories from NBC News:
Follow World News from NBCNews.com on Twitter and Facebook