Anders Behring Breivik acted alone when he killed at least 93 people and wounded nearly 100 in a bombing and shooting rampage, Oslo police said yesterday.
As investigators pored over a 1,500-page internet tract by Mr Breivik, who is 32, looking for clues to Friday's atrocity, Norway's King Harald V, Queen Sonja and the prime minister Jens Stoltenberg led the nation in mourning at an emotional memorial mass in Oslo Cathedral.
Mr Breivik is expected to appear in court in Oslo today. He has admitted carrying out the bombings and shootings, but says his actions were neither criminal nor reprehensible. His lawyer, Geir Lippestad, said: "He feels that it was cruel to have to carry out these acts but that, in his head, it was necessary."
Police detained several people yesterday in a raid on an Oslo property thought to be connected to the attacks, but released them later.
Some witnesses had reported seeing a second gunman during the attack, but the Oslo police commissioner, Sveinung Sponheim, said: "During questioning, he said he acted alone. We will try to verify this through our inquiry."
In the internet tract posted on the day of the attack, Mr Breivik wrote that he had been preparing the "martyrdom operation" since at least autumn 2009. Police said the tract ranted against Muslim immigration to Europe and vowed revenge on "indigenous Europeans" whom Mr Breivik accused of betraying their heritage.
It ends with a detailed description of the plot, ending with a note dated 12.51pm on Friday: "I believe this will be my last entry."
A 12-minute video clip posted on YouTube with the same title as the manifesto featured slides suggesting Europe was being overrun by Muslims. One image showed the BBC's logo with the "C" changed into an Islamic crescent. Another declared that the end result of the left's actions would be an "EUSSR".
The video also featured photographs of Mr Breivik dressed in a military uniform and in a wetsuit pointing an assault rifle.
Meanwhile Norway was struggling to understand how a country that is a beacon of peace could experience such bloodshed on its soil. Mr Stoltenberg told mourners in Oslo Cathedral that the names and photographs of the victims would soon be released and "the scale of the evil will then emerge".
He told the hushed congregation that despite the tragedy Norway would demonstrate "more democracy, more openness, more humanity, but without naivety".
"We are a small country but we are a proud people," he said, and Norway "will never abandon its values".
After the service, people sobbed and hugged one another in the streets as they streamed out of the cathedral. Many lingered over a memorial of flowers and candles. In Friday's two attacks at least seven people were killed in a car bomb blast outside government buildings in Oslo and a further 85 were shot dead on the nearby island of Utoeya, where a Labour party youth meeting was being held.
The death toll rose to 93 after one of those wounded in the attacks died in hospital. The toll could rise further as the search continued for four or five people still missing from the island, aided by a mini-submarine and Red Cross scuba divers.
Harrowing testimony emerged from the summer camp where scores of youngsters were mown down,
Stine Haheim, a Labour Party politician who was on the island, said Mr Breivik had carried out his killings methodically. "He was very calm. He was not running, he was moving slowly and shooting at every person he saw," she said.
Other witnesses at the island youth retreat described how Mr Breivik lured them close by saying he was a police officer before raising his weapons. People hid and fled into the water to escape the rampage; some played dead. "Many of those who have died were friends," Mr Stoltenberg said at the memorial mass. "I know their parents and it happened at a place where I spent a long time as a young person … it was a paradise of my youth that has now been turned into hell."
Norway's police have revealed that the near-sinking of a police boat and a decision to await a specially armed unit from Oslo some 45 kilometres away delayed police getting to the island of Utoeya.
Erik Berga, police operations chief in the northern Buskerud County, said: "When so many people and equipment were put into it, the boat started to take on water, so that the motor stopped," said.
The killer went about his deadly work undisturbed by police for an hour after the first reports of gunfire, other police officials said yesterday, revising a previous estimate of about 90 minutes.
Sissel Hammer, the police chief in Hoenefoss, said she understood why critics "think it took too long for the police to come", but said they had moved as quickly as possible.
On Saturday, the acting police chief in Oslo, Sveinung Sponheim, said the killer had spent almost 90 minutes firing at young Labour Party members as they fled around the island or dived into the large Tyrifjord lake. Mr Sponheim said yesterday his previous estimate was "a bit high" and defended his special anti-terror unit's decision to travel some 45km to the scene by road instead by helicopter.
"It was faster going by car," he said, "because we would have had to get a helicopter from the base down south and that would have taken longer". He said the only helicopter available to the Oslo-based unit was 50 to 60km south of the capital.
* With reporting by Agence France-Presse, Associated Press and Bloomberg News