Anders Behring Breivik pleaded not guilty on Monday at his trial after the prosecution had spent more than an hour reading out the names, ages, injuries and cause of death of the 77 killed, as well as details of 42 people seriously injured in the July 22 attacks.
Breivik showed no emotion when prosecutor Inga Bejer Engh read the 19-page indictment. But some of the survivors of the attacks present at the court wept while Engh read the details, and a young girl broke down during a recess.
Unexpectedly, Breivik, however, shed tears before the lunch recess when prosecutor Svein Holden showed the court a 12-minute video that the defendant had made.
The video was "a short version" of a 1,500-page manifesto that Breivik published online shortly before the attacks, Holden said. The prosecution intended to refer to a section, titled Declaration of Preemptive War, of Breivik's manifesto.
The manifesto was emailed to 1,002 email addresses, Holden said, adding the address list contained about 8,100 addresses.
Norwegian public broadcaster NRK opted not to show the video in its live coverage.
Holden also showed footage from surveillance cameras showing the effects of the bomb that Breivik set off near the government headquarters. The court had earlier ruled that this would not be shown by broadcasters due to the gruesome images.
Holden also gave information of Breivik's activities and membership in various groups from 1995 until his arrest - including the Knights Templar organisation whose existence the prosecution disputed.
The prosecutor said Breivik bought items including a uniform, weapons and ammunition, and material for a bomb, and showed the court a badge emblazoned with the text "Marxist hunter" and a false police ID with Breivik's photo.
Breivik made a defiant Nazi-style salute, minutes before his trial opened in Oslo.
He then greeted prosecutors Engh and Holden, as well as the four court-appointed psychiatrists who were set to follow the proceedings scheduled to last 10 weeks.
Breivik, dressed in a dark suit, was seated between his attorneys Geir Lippestad and Vibeke Hein Baera as the hearing began.
"I am a writer," he protested when Judge Wenche Elizabeth Arntzen asked him to state his name, age and occupation, noting he had likely been unemployed since being taken into custody.
"I don't recognise the Norwegian justice system since it has a mandate from parties that support multiculturalism," Breivik said, adding however that he had no formal complaint against the court.
He pointed out that Arntzen was an acquaintance of former justice minister Hanne Harlem and the sister of ex-prime minister Gro Harlem Brundtland, a former Labour Party leader.
Arntzen said this would be duly noted.
Breivik is due to give his testimony on Tuesday.
"It is a special day to see a person who has caused so much pain, but we have prepared for it," Trond Henry Blattmann, who heads a July 22 support group, told broadcaster NRK before the trial began.
The trial was held amid tight security.
The area around the Oslo District Court was cordoned off and all visitors to the court - including media, survivors and the public - had to pass through security checks.
Sniffer dogs on Sunday searched the building, which was guarded by armed police officers, while the airspace over Oslo was closed for small planes.