Anders Behring Breivik arrived and left in an armoured Mercedes via a back entrance to the courthouse where he was to face arraignment after his arrest Friday following the twin attacks that killed as many as 93 people.
"The hearing is over, the room is empty," said a court official in the Norwegian capital. It lasted about 40 minutes.
TV2 television showed grainy images of a shaven-headed Behring Breivik wearing a red top being taken from the court, almost unrecognisable as the man with a mop of blond hair featured in photographs in his own lengthy Internet manifesto.
A young Norwegian Muslim told AFP he kicked at the car in memory of a friend killed in the shooting massacre on Utoeya island.
Judge Kim Heger was to decide on the prosecutor's call for him to be placed in detention for eight weeks as the investigation proceeds -- double the normal, renewable period -- but nothing emerged immediately of what had happened in court. People waiting to catch a glimpse of him cried "traitor" and "bloody killer," Norway's NTB agency said.
Behring Breivik's lawyer, Geir Lippestad, came in through the main entrance, having to force a passage through hundreds of journalists waiting since early morning.
As the nation struggled to absorb the impact of its worst postwar tragedy, thousands of people bowed their heads in silence outside Oslo's main university at a ceremony led by Prime Minister Jens Stoltenberg and King Harald V.
"To remember the victims who died at the government's headquarters and on the island of Utoeya, I declare a minute of silence," said Stoltenberg on the stroke of midday before he opened a book of condolence.
The country's train stations closed and the stock market halted trading. Nordic neighbours Sweden, Finland, Denmark and Iceland also held a minute's silence and flew national flags at half-mast.
"It was an attack against the very values that our countries are built upon. It was an attack against all of us," said Danish Prime Minister Lars Loekke Rasmussen.
Anders Behring Breivik has already confessed to the killings but denied criminal responsibility, according to his lawyer.
Lawyer Lippestad has said the 32-year-old has said he had planned Friday's car bombing and mass shooting over a long time and executed the attacks single-handedly.
Behring Breivik's lawyer Geir Lippestad said earlier that his client had two wishes: "The first is that the hearing is public, and the second is that he may attend in uniform."
Before the attack, Behring Breivik wrote a 1,500-page manifesto, datelined London. He boasted he was one of up to 80 "solo martyr cells" recruited across Western Europe to topple governments tolerant of Islam, it said, adding that Scotland Yard was now trying to establish if he had recently visited London.
At least seven people died in an initial car bombing outside the prime minister's office, in a calculated distraction for police allowing Behring Breivik to shoot scores of youngsters attending a summer camp on the island of Utoeya, 40 kilometres away (25 miles).
The official toll from the island currently stands at 86 although police have said the figure could be revised downwards.
Names and photographs are to be released shortly of those who died, including offspring of senior ruling party figures.
An emotional Stoltenberg said at a memorial service on Sunday that the full extent of the "evil" perpetrated Friday would emerge when the victims' names and their photographs are released.
It emerged Monday that the half-brother of Norway's Princess Mette-Marit -- an off-duty policeman -- was one of the victims of the gun attack.
Behring Breivik currently has only the status of "official suspect," meaning he will not learn actual charges until the investigation is concluded with police still hunting for possible accomplices.
But the attacks have triggered calls for Norway to reinstate the death penalty. The maximum prison sentence in Norway is 21 years, meaning -- if found guilty -- the accused could be awarded just 82 days per killing.
Behring Breivik acknowledged in his tract that he would be deemed a "monster," but said it was designed to end a centuries-long Muslim colonisation of Europe.
Although he told investigators he acted alone, prosecutors stressed they had yet to uncover a motive -- despite the manifesto claims.
Part diary, bomb-making manual and Islamophobic rant, the tract details the self-styled Knight Templar's "martyrdom operation" including a call for believers to spawn as many children as possible in order to generate a pool of future fighters in a Christian war he likens to a medieval crusade.
During weekend interrogation, Behring Breivik told police that Europe's deadliest attacks since the 2004 Madrid bombings, were "cruel" but "necessary."
Nevertheless, lawyer Lippestad said his client felt he had done "nothing reprehensible."
Police have faced loud criticism over the hour it took them to reach the island, during which victims -- some shot again in the head to make sure they were dead, according to witnesses -- died at a rate of more than one per minute.