"He wants to be held responsible," lawyer Geir Lippestad told the daily newspaper Aftenposten. "He thought about what he wanted to say to the judges and so has prepared a few lines for every outcome."
Lippestad said he was unsure if Breivik would be able to address the Oslo court on Friday, when five judges will announce whether they consider the 33-year-old legally responsible for his crimes.
The verdict determines whether Breivik will spend a long sentence behind bars or in a closed psychiatric ward.
On July 22nd 2011, Breivik set off a car bomb outside the government offices in Oslo, killing eight people, before going to the island of Utøya, north-west of the capital, where he spent more than an hour gunning down another 69 people, mostly teenagers, attending a Labour Party youth camp.
Breivik has confessed to the killings but his 10-week trial has been one of the most compelling in Norway's history as the court tries to delve into his mindset.
Another of his lawyers, Tord Jordet, told the tabloid Verdens Gang that his client is working on a sort of autobiography in which he would detail his preparations for the attacks and include revelations about the mysterious Knights Templar.
Breivik claims he began his ideological crusade in 2002 as part of the Knights Templar -- an organisation whose existence police have never been able to confirm.
The book "will contain more information than what he told the police," Jordet said, adding that the book would be written in English and available next year.
Breivik has presented himself to the court as a writer and wrote a 1,500-page manifesto he published online just before the massacre.
Breivik has said he would not appeal the case if judges find him sane.