The man accused of killing at least 76 people in a shooting massacre and car bombing in Norway had been on an intelligence watch list since March, according to reports.
The Norwegian newspaper VG Nett claims Anders Behring Breivik had been put on the list after illegally buying large amount of chemicals online from a Polish retailer.
Sky's Ian Woods said the Norwegian intelligence service had not acted on the information about because they did not believe it was "relevant".
In his first court appearance since the horrific attacks on Friday, Breivik admitted he was responsible but pleaded not guilty.
He also revealed that there are "two further cells" in his terror organisation which the judge said will be investigated.
He had previously said he was acting alone and police currently have no other suspects.
But in a press conference officers said they "cannot completely rule out that someone else was involved".
In a statement he said he had carried out the attacks because he wanted to "save Norway and Western Europe from a Muslim takeover".
He accused the Labour party of "mass imports of Muslims" and said the objective behind the terror plot was to give a "sharp signal to the people".
The 32-year-old said his bombing of government buildings in Oslo and shooting spree at a summer camp on Utoya island for Labour's youth wing was aimed at deterring future recruitment to the Labour party.
Friday's tragedy started when Breivik set off a car bomb near government headquarters in Oslo.
Police have said the number of people killed in the blast has increased to eight, with a further 30 injured.
:: See more pictures from Friday's attacks here
Ninety minutes later Breivik opened fire on hundreds of teenagers assembled for the youth camp on Utoya. The death toll for that massacre has now been revised down to 68.
The overall total for both attacks had previously been given as at least 93.
It is hoped that identification of the victims will be completed by Thursday.
Several others are said to still be missing and 50 officers are searching for evidence on Utoya.
Sniffer dogs are also being used to search wreckage from the bomb in Oslo.
Breivik has been charged with terrorism offences and will be remanded in custody for eight weeks, including spending the first four weeks in solitary confinement with no visitors, letters or access to media.
Judge Heger said it was important Breivik could not communicate with other people.
He also refused his request to wear a uniform in court. Breivik was dressed as a policeman when he carried out the shootings on Utoya, 20 miles (35km) from Oslo.
The prosecution said Breivik had behaved calmly and did not seem to be affected by events. They said he understood that he would spend the rest of his life behind bars.
His father has been reported as saying his son should have killed himself instead of surrendering to police.
The self-styled crusader had asked for an open hearing so he could explain his actions to the public.
But the judge ruled the court would be closed after police and prosecutors voiced concerns he might try to send coded messages to fellow extremists.
In a statement the court said: "It is clear that there is concrete information that a public hearing with the suspect present could quickly lead to an extraordinary and very difficult situation in terms of the investigation and security."
More than 60,000 had signed up to a Facebook page called "Shut the doors on Monday", calling on the court to deny Breivik the publicity he craves.
A huge crowd of media and angry members of the public gathered outside Oslo Court House in anticipation of the Norwegian's appearance.
None of his victims has been named except for one - 51-year-old Trond Berntsen, the stepbrother of crown princess Mette-Marit.
A policeman, he was apparently on the island of Utoya as a private guard for the gathering.
Meanwhile, gendarmes were called to the home of Breivik's father in Cournanel in southern France - the pair have apparently not been in touch for several years.
Earlier, hundreds of people gathered in Oslo for a minute's silence and to lay flowers or light candles for the victims.
:: Click here for the official online book of condolence (in Norwegian):
Calling himself a crusader against a tide of Islam, Breivik produced a 1,500-page "terrorist manifesto" datelined London to explain his thinking and proposed actions.
According to the Daily Telegraph, he claimed in the manifesto his mentor was an Englishman called Richard.
He also boasted that he was one of up to 80 "solo martyr cells" recruited across Western Europe to topple governments tolerant of Islam.
British police experts have been drafted in to help probe any links Breivik may have with European far-right organisations.
And David Cameron has chaired a National Security Council meeting with the Government's top security advisers to discuss Britain's vulnerability to a Norway-style terrorist attack.
Political correspondent Sophy Ridge said there is pressure on the Prime Minister to place more resources on tackling far-right groups in Britain.
Breivik's lawyer Geir Lippestad said: "He has been politically active and found out himself that he did not succeed with usual political tools and so resorted to violence."
He went on: "I await a medical assessment of him.
"He explains himself fairly calmly but every now and then expresses emotion. He buries his head in his hands.
"He has said that he believed the actions were atrocious but that in his head they were necessary."
The attacks have left Norway, a small and wealthy country unused to political violence, in a state of shock.
There has been growing anger among the far right on a number of issues including immigration.
Immigration has happened quickly in Norway and it has changed the demographic. The far right argue that they have no mainstream political representation.
:: Follow all the latest news on the Norway attacks in the blog below: