Anders Breivik has begun to serve his prison sentence for the massacre of 77 people in bomb and gun attacks in Norway last year.
At the end of his sentencing hearing on Friday, Breivik said he will not appeal against the sentence because this would "legitimise" the court.
He also apologised to "militant nationalists" for not having killed more people in the attacks in July last year.
Breivik's gruesome and defiant statement could mark the end of a legal process which haunted Norway for 13 months.
Prosecutors said they had not decided whether to appeal against the ruling by Oslo's district court, which declared the right-wing extremist sane enough to be held criminally responsible for attacks "unparalleled in Norwegian history".
"Since I don't recognise the authority of the court I cannot legitimise the Oslo district court by accepting the verdict," Breivik said. "At the same time I cannot appeal the verdict, because by appealing it I would legitimise the court."
Then, Breivik said he wanted to issue an apology but it was not for the victims, most of them teenagers gunned down in one of the worst peacetime shooting massacres in modern history. "I wish to apologise to all militant nationalists that I wasn't able to execute more," said Breivik.
Earlier on Friday, the five-judge panel in the Oslo district court convicted Breivik, 33, of terrorism and premeditated murder and ordered him to be jailed for a period between 10 and 21 years, the maximum allowed under Norwegian law.
Breivik smiled with apparent satisfaction when Judge Wenche Elisabeth Arntzen read the ruling, declaring him sane enough to be held criminally responsible and sentencing him to "preventive detention", which means it is unlikely he will ever be released.
The sentence brings a form of closure to Norway, which was shaken to its core by the attacks on July 22, 2011, because Breivik's lawyers said before the verdict that he would not appeal against any ruling that did not declare him insane. But it also means Breivik got what he wanted - a ruling that paints him as a political terrorist instead of a psychotic mass murderer.