The rightwing extremist who confessed to the mass killings in Norway boasted in court on Monday that there were two more cells from his terror network still at large, prompting an international investigation for collaborators.
After Anders Behring Breivik pleaded not guilty, despite admitting that he had carried out the attacks in Oslo and on Utøya island, officials said it was possible he had not acted alone.
Prosecutor Christian Hatlo said Breivik had been calm in court and "seemed unaffected by what has happened", adding that the suspect had told investigators during his interrogation that he never expected to be released.
"We can't quite rule out that someone else was involved. This is partly based on the information that there are two other cells," Hatlo said.
The prosecutor said he could not discuss whether Breivik had organised the cells or whether he was working alongside them. Police have said they have no other suspects at present.
It also emerged on Monday that Norway's police security service had been alerted to a suspicious chemical purchase by Breivik in March, but had decided not to investigate further.
Police also lowered the previously announced death toll, saying 68 people died on Utøya, not 86 as previously stated. Eight died in the bomb attack in Oslo, taking the total number of fatalities to 76.
Breivik's plan to use the courtroom to create a global platform for his Islamophobic message failed when the judge, Kim Heger, ordered that the arraignment be held in camera. Prosecutors said the hearing was held behind closed doors because of security concerns, heightened after Breivik cited the possible existence of a wider group of far-right backers.
Breivik was remanded in custody for eight weeks, with the first four to be in solitary confinement – meaning he will be allowed no visitors other than his lawyer, and will have no access to newspapers, other media, or letters. Police said a trial may not take place for up to one year.
Breivik's organisation, which he claimed to have founded in London nine years ago, is supposedly a reconstituted version of the medieval Knights Templar.
Experts and intelligence agencies have voiced concern over the threat from pan-European rightwing terror groups since Breivik's attacks last Friday.
Breivik was said to have been placed on an intelligence watch list in March after apparently buying chemical fertiliser from a Polish company. Janne Kristiansen, the chief of Norway's police security service, told national broadcaster NRK that the purchase had set off an alert because the company was under scrutiny. But since the transaction was legal, security police did not have a reason to investigate further.
It was reported that Breivik was with a second person when he also tried to buy fertiliser earlier this year.
Breivik was said to have told police that he intended to "hit" Gro Harlem Brundtland, a former Norwegian prime minister and Labour party leader, who visited Utøya hours before the attack.
A spokesman for Brundtland said she had been on the island until 3pm on Friday, attending the ruling Labour party's youth camp, and left before the shooting started. Breivik said he had been delayed reaching the island but did not say why, police said. In his self-proclaimed "manifesto", Breivik accused Labour of threatening Norwegian culture by allowing the "mass import of Muslims".
Norway continued to mourn its dead on Monday night with 100,000 people gathering in the capital for a march and vigil led by the prime minister, Jens Stoltenberg. Other rallies were held around the country.
A vehicle carrying Breivik to the court hearing was beaten by angry onlookers who jeered and shouted abuse.
The revulsion was shared by Breivik's estranged father. "I don't feel like his father," said Jens David Breivik, who lives in France. "How could he just stand there and kill so many innocent people and just seem to think that what he did was OK? He should have taken his own life, too. That's what he should have done," he told Sweden's Expressen newspaper.
Breivik's "manifesto", entitled a European declaration of independence, was posted on the internet hours before the attacks. In it, he said he would use his arrest to mount a media blitz to publicise his cause. If he survived the attacks and was captured, that would "mark the initiation of the propaganda phase", he wrote.
Breivik's lawyer, Geir Lippedstad, said: "He has been politically active and found out himself that he did not succeed with usual political tools and so resorted to violence."
Hatlo, the prosecutor, said Breivik was calm and "seemed unaffected by what has happened".
The prospect of an enduring threat linked to Breivik was one of many revelations following the 32-year-old's court appearance in which he said his motive for the attacks was to save Europe from a Muslim takeover.
Criticism of the police response grew on Monday as survivors from Utøya told of their wait for help. Police swat teams took an hour to get to Utøya after the first alert was issued, hampered in part by a lack of helicopters. It emerged that a boat heading for Utøya had to turn back after it began to take on water due to its heavy load of police officers and equipment.