In a single message on his Twitter social media account, he recently paraphrased British philosopher John Stuart Mill, saying, "One person with a belief is equal to a force of 100,000 who have only interests."
Earlier Saturday, a farm cooperative said it sold six tons of fertilizer, a product sometimes used in bombmaking, to Breivik in May.
Breivik managed an organic farm called Breivik GeoFarm, growing vegetables, melons, roots and tubers. The cooperative described the size of his fertilizer purchase as a "relatively standard order" for a farm like his but alerted authorities about the sale when it learned he was a suspect in the bombing. Norwegian media say the massive bomb that exploded at the government building was made from fertilizer.
Police say Breivik is cooperating in their investigation. One police official said the suspect made it clear that he "wants to explain himself."
The revelation about Breivik's fertilizer purchase came as Norwegian police investigated the possibility there might have been a second gunman involved in the assault on the youth camp on idyllic Utoeya island. Several hundred teenagers had gathered there as part of a program sponsored by the country's ruling Labor Party.
Footage of youth summer camp, Oslo bombing, and Prime Minister Jens Stoltenberg
While police questioned Breivik, the country's national news agency NTB said Saturday that witnesses on Utoeya told police two people were involved. The man already in custody was disguised as a policeman, wearing a sweater with a police emblem on it, but the witnesses said the second man was not. Police said they do not know whether Breivik acted alone and are continuing their investigation.
Norway reeled with horror at the twin attacks.
Prime Minister Jens Stoltenberg called the assaults, the worst in Norway since World War II, "a national tragedy, a nightmare." He called the bombing and shootings "bloody and cowardly attacks" and said Utoeya has been turned from "a paradise into hell."
Police are searching the lake surrounding the island about 30 kilometers north of Oslo for more bodies.
Even as details emerged about Breivik's political views, Mr. Stoltenberg said it was "too early" to speculate on what the motive might have been for the attacks and police have also declined to assign a reason.
Mr. Stoltenberg said the "brutal" attack on "innocent youths" would not take away Norwegians' feeling of safety. He said safety was a pillar of society that Norwegians had taken for granted, and he stressed that the main focus is on saving the lives of those hurt in the attacks.
Norwegian Foreign Minister Jonas Gahr Store said that in addition to the seven deaths the bomb blast caused, nine others were seriously wounded. He said the death toll from the island attack could increase.
Eskil Pedersen, a leader of the Labor Party youth wing and a survivor of the attack, said the group "will not let the terrorist win." He said the group will continue to work hard for the party in honor of those who were killed.
The building that was bombed in Oslo houses the office of the prime minister. He was not there at the time and was not harmed.