As Norwegians try to make sense of the terror attacks that killed 94 people on Friday, many questions remain unanswered:

Were the attacks the work of a lone gunman?

Police say Anders Behring Breivik, who has admitted responsibility for the bomb and gun attacks, claims to have acted alone. Investigations are continuing into unconfirmed reports of a second gunman on the island of Utøya and possible connections between Breivik and far-right international groups. The police chief, Sveinung Sponheim, said they were "not at all certain" whether Breivik had acted alone. "That is one of the things that the investigation will concentrate on." But so far, no evidence has emerged implicating anybody else and police say they have no other suspects at present.

Breivik appears to have been a loner with few friends. He was described by Norwegian media as a rightwing fanatic. His father, who lives in France, said he had had no contact with his son since 1995. Comparisons have been drawn with Timothy McVeigh, who killed 168 people with a truck bomb in Oklahoma City in 1995.

Why did he do it?

Breivik appears to have developed a pathological hatred of the Norwegian "establishment", principally the political class symbolised by the ruling Labour party, whose youth camp on Utøya he attacked. His political views were too extreme for the rightwing Progress party, of which he was once a member.

An ethnic Norwegian, he was strongly opposed to signature government policies favouring multiculturalism. Although an apparent racial supremacist and Islamophobe, he adopted the language of Muslim jihadists.

Agencies reported that a video posted on the YouTube website showed several pictures of Breivik, including one of him in a scuba diving outfit pointing an automatic weapon. "Before we can start our crusade we must do our duty by decimating cultural marxism," said a caption under the video called Knights Templar 2083. The video has been taken down.

A Norwegian website has provided a link to a 1,500-page electronic manifesto and a book which Breivik was said to have written. "Once you decide to strike, it is better to kill too many than not enough, or you risk reducing the desired ideological impact of the strike," the book said.

Breivik's lawyer, Geir Lippestad, said: "He has said that he believed the actions were atrocious, but that in his head they were necessary."

Could more have been done to prevent the attacks?

Police said it took them an hour to stop the massacre on Utøya island, from the moment they were notified of the shootings to the point when they arrested Breivik. "The response time from when we got the message was quick," Sponheim said after criticism that there had been an unacceptable delay. "There were problems with transport out to the island."

One unanswered question is why police drove, instead of using a helicopter. Utøya island is situated in a lake about 26 miles north-west of Oslo.

It was also unclear whether the police had the appropriate equipment and weapons for dealing with a homicidal gunman or gunmen. The government buildings in Oslo appear to have been relatively unprotected compared with their equivalents in London or Washington DC. The bombing and massacre are certain to force a top-level security rethink.

How was the gunman captured?

Police have not given any details of Breivik's capture, but said he gave himself up to armed officers when they arrived on Utøya. Breivik seems to have surrendered without a fight and does not appear to have attempted to escape. This suggests he was determined that his actions would have the maximum political impact, including what is certain to be a high-profile trial.

Breivik does not appear to have tried to turn his gun on himself, as perpetrators of similar mass killings in the US and Britain have done.

.

How will Norwegians respond to the massacre?

The initial reaction among Norwegians has been one of shock that such a tragedy could occur in a traditionally peaceful country where crime rates are low – and that the perpetrator was one of their "own". The sense of national disorientation increased when assumptions that Middle Eastern terrorists or Islamists were responsible proved wrong.

Commentators have begun to talk of the attacks as a defining moment for Norway, marking a "loss of innocence". The prime minister, Jens Stoltenberg, said he was determined Norway would maintain its liberal and progressive traditions. "It's too early to say how this will change Norwegian society," he said. He added that he hoped Norway could maintain its open and democratic society. "Those who try to scare us shall not win."