"This will be extremely difficult, an enormous challenge to listen to his explanations," Geir Lippestad told reporters. "He will not only defend (his actions) but will also lament, I think, not going further."

The 33-year-old right-wing extremist also said he was "pleased" with the results of a new psychiatric probe that found him sane and criminally responsible, contrary to a first official exam that concluded late last year that he was suffering from "paranoid schizophrenia" and therefore criminally insane.

"His first reaction was that he was pleased with the conclusion" of the new expert report, Lippestad told reporters after discussing the new findings with his client.

"He also said he was not surprised, that he had been expecting this conclusion," the lawyer added.

Breivik, who has said being sent to a psychiatric ward would be "worse than death", wants to be declared sane, according to his lawyers, so as not to damage the political message presented in his 1,500-page manifesto published online shortly before the twin July attacks.