The man accused of killing 77 people in a bomb and gun rampage in Norway last summer claimed self-defense on Monday.
"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.
Breivik made the remarks as he went on trial for the July 22 killings to which he has admitted.
Earlier during the proceedings, he raised a clenched fist and said he did not recognize the authority of the court.
He then listened impassively as the prosecutor read the charges against him, describing how dozens of teenagers and young people died from shots to the head and body.
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.
He was not physically restrained in court.
He objected to the judge's friendship with a former justice minister, calling the trial political, Norwegian media reported.
Breivik was charged last month with committing acts of terror and voluntary homicide. He is accused of killing eight people in a bomb attack in Oslo, then going to Utoya Island outside the city and systematically gunning down 69 more people, many of them teens and young adults.
Breivik's trial is expected to last up to 10 weeks. If he is convicted, his punishment will be based on the determination of his sanity. It may not be possible for him to receive the maximum punishment, if he is deemed insane.
"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 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.
Authorities have described Breivik 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.
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 told CNN 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.
He insists 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 a matter of self-defense, 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 and sees himself in the role of a "fantastic, great person who will save Europe."
"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.
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