The Oslo district court is to announce on Friday whether the 33-year-old right-wing extremist will be sent to prison or a closed psychiatric ward for the July 22nd 2011 attacks that killed 77 people.
"He thought about what he wanted to say to the judges and so has prepared a few lines for every outcome," Breivik's lawyer Geir Lippestad told the daily newspaper Aftenposten.
It remains however uncertain if Breivik will be allowed to make any remarks on Friday.
During his 10-week trial that concluded in June, the court was wary of giving Breivik a platform to express his Islamophobic and anti-multicultural ideology, but on several occasions allowed him to speak at length.
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 was one of the most compelling in Norway's history as the court tried to delve into his mind to determine whether he is sane or not.
Another of Breivik's lawyers, Tord Jordet, told the tabloid Verdens Gang that his client is working on a sort of autobiography, which would contain details on how he prepared for the attacks and revelations about the mysterious Knights Templar organisation.
The book would focus on his life as of 2002, when Breivik claims he began his ideological crusade as part of the Knights Templar, though police have never been able to confirm the existence of the network of far-right militants that Breivik claims to have founded in London.
The book "will contain more information than what he told the police," Jordet said, adding that it would be written in English and finished next year, although it is not yet known whether it would be published.
Breivik is also reportedly known to be working on two other books, one on his ideology and another on his vision of the future.
The gunman has presented himself to the court as a writer and published a 1,500-page manifesto online just before the massacre. It contained elements about his ideology, his life and details of how he readied himself for the attacks.
He wants to be found sane so that his beliefs will not be considered the ravings of a lunatic, and has said he would not appeal the case if judges rule that he is of sound mind.
Even though Breivik has confessed to the crimes, he pleaded not guilty and said his acts were "cruel but necessary" to protect Norway from the multiculturalism his victims had embraced.
A first court-ordered psychiatric evaluation concluded he was suffering from a psychosis, which would mean he would be sent to a mental asylum.
But a second opinion found he was sane enough to be considered criminally responsible, meaning he could be sentenced to prison.
Regardless of the verdict, Breivik is expected to live a very regimented life at the high-security Ila prison near Oslo, which is building a new wing to serve as a mini-hospital in case he is ordered to undergo psychiatric care.
On Wednesday, the facility published photographs giving a peek into Breivik's current conditions at the prison.
He has access to three cells, each measuring eight square metres, with one to sleep in, one for physical exercise, and one workspace that has a laptop -- without internet -- nailed to a desk.
"We are ready to receive Mr. Behring Breivik if he is sentenced to preventive detention (prison) and also if he is sentenced to compulsory psychiatric care," the governor of Ila prison, Knut Bjarkeid, said in a statement.