Anders Behring Breivik, who took 77 lives in attacks last July, said on Monday he wanted to apologise for killing "innocent" people in his Oslo bombing, but not for the Utoeya massacre.
Breivik said: "I would like to offer a large apology" to those who were just passing by and had no political connections, but who were injured or killed in the bombing of an Oslo government building.
Eight people died in that attack.
When prosecutor Enga Bejer Engh asked if he could say the same to any of the 69 people -- mainly teens -- he slaughtered in his shooting massacre on the nearby island of Utoeya after the bombing, Breivik said: "No, I do not."
He reiterated that the youngsters attending a summer camp hosted by the ruling Labour Party's youth wing were "legitimate targets", as they were "political activists" working for the "deconstruction of Norwegian society."
"This is a small barbarity to avoid a larger barbarity," he insisted on Monday.
He knew what he had done and understood he had ruined the lives of many people, but had "decided not to absorb this ... in order to survive."
On the sixth day of his trial, Breivik continued answering questions about the deadliest massacre ever committed by a sole gunman, after providing chilling details on Friday of how he calmly walked across the island, picking off his victims , shooting most of them point-blank in the head.
Breivik had originally been scheduled to testify on Monday about his sanity, which is the main issue of contention during the 10-week trial. But that was postponed so he could finish testifying about Utoeya.
The 33-year-old right-wing extremist has been charged with "acts of terror" and faces either 21 years in prison -- a sentence that could thereafter be extended indefinitely if he is still considered a threat to society -- or closed psychiatric care, possibly for life.
A first court-ordered psychiatric exam found him insane, while a second opinion came to the opposite conclusion.
The confessed killer wants to be found sane and accountable for his actions, so that his anti-Islam ideology, as presented in the 1,500-page manifesto he published online just before the attacks, will be taken seriously and not considered the ravings of a lunatic.
He has said that court-ordered psychiatric care would be "worse than death".
The five judges will have to consider the two contradictory psychiatric evaluations presented to the court, and determine whether he is sane and accountable when they hand down their verdict sometime in July.