Anders Behring Breivik is due to appear in court charged with terrorism following the Oslo explosion and Utoya shootings on Friday which are now known to have claimed at least 93 lives.
Breivik's lawyer Geir Lippestad said the 32-year-old Norwegian had confessed to the twin attacks but denied criminal responsibility and said he was motivated by a desire to bring about a revolution in Norwegian society.
A manifesto that Breivik is believed to have written ranted against Muslim immigration to Europe and vowed revenge on "indigenous Europeans" who he accused of betraying their heritage.
In a chilling allusion to the fact that the double tragedy which killed 93 people could have even been greater, police said Breivik still had "a considerable amount" of ammunition for both his guns - a pistol and an automatic rifle - on him when he surrendered.
The manifesto - which police are looking at - was published online on the day of the attacks and it ranted that the European elite, "multiculturalists" and "enablers of Islamisation" would be punished for their "treasonous acts".
Parts of the manifesto were taken almost word for word from the writings of "Unabomber" Ted Kaczynski.
The passages copied by Breivik appear in the first few pages of Kaczynski's manifesto. Breivik changed a Kaczynski screed on leftism and what he considered to be leftists' "feelings of inferiority" - mainly by substituting the words "multiculturalism" or "cultural Marxism" for "leftism".
Kaczynski is in federal prison in the US for sending letter bombs which killed three people. Breivik did not cite Kaczynski, though he did credit others whose writings he used.
Police have not confirmed that Breivik wrote the document, but his lawyer referred to it and said Breivik had been working on it for years.
The treatise ends with a detailed description of the plot, ending with a note dated 12:51 p.m. on July 22: "I believe this will be my last entry."