OSLO, Norway (CNN) -- The man accused of killing 77 people in a bomb-and-gun rampage in Norway last summer admitted Monday that he had committed the acts but said he was not guilty.
"I acknowledge the acts but do not plead guilty, and I claim I was doing it in self-defense," Anders Behring Breivik told a court in Oslo, Norway. The court recorded a plea of not guilty for him.
Breivik's trial, which began Monday, is expected to last up to 10 weeks. If convicted, the court will base his punishment on a determination of his sanity. It may not be possible for him to receive the maximum punishment, if he is deemed insane.
Prosecutors played a recording of a terrified girl phoning for help during the shooting spree that left 69 people dead, many of them teens and young adults. The audio was punctuated by constant firing in the background.
They also showed security camera footage of the central Oslo bomb blast that killed eight people, images that participants in the trial watched with ashen faces.
Breivik was charged last month with committing acts of terror and voluntary homicide.
Authorities have described him as a right-wing Christian extremist. A 1,500-page manifesto attributed to him and posted on the Internet is critical of Muslim immigration and European liberalism, including Norway's Labour Party.
As the trial opened, he raised a clenched fist and said he did not recognize the authority of the court.
He called the trial political and objected to the judge's friendship with a former justice minister.
"I do not recognize the Norwegian court. You've gotten your mandate from political parties that support multiculturalism," he said.
"OK, we will make a note of that general objection," Judge Wenche Elizabeth Arntzen said curtly.
Breivik later clarified that he was not raising a formal objection.
He listened impassively as prosecutor Inga Bejer Engh read the charges against him, describing how dozens of teenagers and young people were shot to death.
Breivik, in a black suit and jawline beard, read the indictment as the prosecutor spoke, showing no reaction as she listed the injuries the victims suffered on Utoya Island.
Prosecutors outlined his life before the killings, showing a photo of the messy room where he lived at his mother's house, listing his six failed businesses and referring to his many hours playing the online game "World of Warcraft."
Prosecutors said he had "no job, no salary, no money from the government" and was "living off his savings."
He smiled briefly when his "Warcraft" character was shown, one of thew few times he showed emotion on Monday.
He also appeared to be overcome with emotion, fighting back tears, when part of his video manifesto "Knights Templar 2083" was played in court.
Prosecutors also showed a badge Breivik has been seen wearing. It says "Marxist hunter" and "multiculti traitor hunting permit 1998 - 2083."
He was not physically restrained in court.
"It's going to be 10 weeks of hell ... to hear this man, to hear his explanation of why he did it and how he did it," said Trond Henry Blattmann, whose son was killed on Utoya Island.
In November, prosecutors said psychiatrists had determined that Breivik was paranoid and schizophrenic at the time of the attacks and during 13 interviews experts conducted with him afterward.
However, the court sought a second opinion because of the importance of the question of sanity to Breivik's trial.
In a report released this month, two court-appointed psychiatric experts said Breivik was sane at the time of the alleged crimes.
The victims on Utoya Island were among 700 mostly young people attending a Labour Party camp.
It was the same camp Norwegian Prime Minister Jens Stoltenberg said he had attended every summer since 1974.
"I think that one of the main messages from Norway after the tragedy ... was that we were going to protect our democracy. And part of our democracy is the divisions of responsibilities between the government and the courts. It's up to the courts to decide whether this man is going to be sentenced or not, whether he is insane or not. It's not a question which is going to be decided by politicians. That's part of our democratic society," Stoltenberg said.
Breivik insists that nobody could believe that he was insane and describes questions about his mental condition as ridiculous, his attorney, Geir Lippestad, has said.
Breivik claims the shooting rampage was meant to save Norway from being taken over by multicultural forces and to prevent ethnic cleansing of Norwegians, Lippestad said.
Tore Bjorgo, a terror expert and professor at Norwegian Police University College, said Breivik appears to be overly concerned about his self-image
"It's we who should decide what kind of a society we want; it's not the terrorists. And the logic of terrorism is to try to provoke responses to get people to act in ways the terrorists want and it was important that we didn't do that. We didn't go down that road, and that was, I think, a big victory," he said.
CNN's Per Nyberg and Marilia Brocchetto contributed to this report.