Norwegian police increasingly believe the man who confessed to killing 77 people in last month's attacks planned and committed them on his own, a prosecutor has said.
Anders Behring Breivik detonated a bomb outside government buildings in Oslo on July 22, killing eight people, followed by a massacre at a youth camp on an island outside the capital where he shot dead 69 others.
There was initial speculation that others were involved in the attack, but prosecutor Christian Hatlo said that after 40 hours of questioning police are fairly certain Breivik acted alone and that he appears to be telling the truth.
Hatlo said police have been able to verify much of what Breivik told them about the attacks, and that they had not discovered "any direct lie, yet".
"That is also why we, with a certain confidence, can say that he was alone, but I have to emphasise that we have not concluded yet," Hatlo said.
Last week, police also said they believed Breivik acted alone, but they searched his computer and mobile phone records for any signs of contact with other right-wing extremists who may have helped or influenced him.
Law enforcement agencies in other countries have also assisted Norway, and in the US, they interviewed Breivik's sister in Los Angeles. Hatlo said all the information they received from abroad also pointed to the 32-year-old having acted alone.
"Nothing supports suspicion about other cells (being involved), rather the opposite," Hatlo said. He declined to give details.
Breivik said, in a 1,500-page manifesto posted online, that the attacks were an attempt at cultural revolution, aimed at purging Europe of Muslims and punishing politicians that have embraced multiculturalism.
He told police he was part of an anti-Muslim militant network and that there are two other cells in Norway and several abroad, but that they were not involved in the attack.