Profile of the suspect
Breivik is described as an ethnic Norwegian. Photos of him on social networking sites and local media show him with pale, clean-cut features and straight blonde hair.
According to messages posted on social networking sites and statements made to Norwegian media by persons who know him, Breivik, a conservative Christian, holds extreme right-wing views.
He enjoys weightlifting, video-games and hunting, holds strongly nationalist and anti-Muslim views, and is against multiculturalism.
Breivik posted a 1,500-page manifesto on the Internet Friday, describing the planning of the attacks and his personal philosophy.
Online searches revealed that Breivik has previously been in contact with far-right groups in Britain. He has also made derogatory remarks about leading Norwegian politicians.
According to Norwegian media, Breivik's parents divorced when he was very young and he has subsequently had almost no contact with his father, who now lives in southern France.
Both his father and mother said they are bewildered and appalled to hear of their son's violent actions.
Breivik had studied at an Oslo-based business college, and wanted to be an entrepreneur. But after failing at several businesses, he moved out of Oslo in 2009 and set up a farm in Asta, some 130 km north of the capital.
Police say six tons of fertilizer were delivered here in May and believe they may have been used in making explosives for Friday's bomb attack.