- Anders Breivik is charged with voluntary homicide and committing acts of terror
- He wants to be ruled sane, and says he acted out of "necessity" to stop multiculturalism
- Prosecutors want him to be acquitted on insanity grounds and held in a psychiatric unit
- Survivors of Breivik's gun rampage testified during his 10-week trial earlier this year
Oslo, Norway (CNN) -- The verdict is due Friday in the trial of Anders Behring Breivik, the man who killed 77 people in a bomb attack and gun rampage in Norway just over a year ago.
Breivik is charged with voluntary homicide and committing acts of terror over the attacks in Oslo and Utoya Island on July 22, 2011.
The issue of Breivik's sanity, on which mental health experts have given conflicting opinions, will be central to the court's ruling.
Breivik, who boasts of being an ultranationalist who killed his victims to fight multiculturalism in Norway, wants to be ruled sane so that his actions are not dismissed as those of a madman.
He says he acted out of "necessity" to prevent the "Islamization" of his country.
But prosecutors have asked that Breivik, 33, be acquitted on the grounds of insanity, in which case he would be held in a secure mental health unit.
The verdict will be delivered at Oslo district court by a panel of five judges.
In the course of the 10-week trial, which wrapped up in June, the court heard chilling evidence from some of those who survived Breivik's shooting spree on Utoya Island, in which 69 people died -- most of them teenagers attending a Labour Party summer youth camp.
In his own testimony, given without any display of emotion, Breivik recounted firing more bullets into teenagers who were injured and couldn't escape, killing those who tried to "play dead" and driving others into the sea to drown.
His fertilizer bomb attack against government buildings in Oslo also killed eight people and injured many more.
He blamed the Labour Party for promoting multiculturalism in Norway.
Several outcomes are possible Friday. If Breivik is fully acquitted on the grounds of "necessity," as urged by his defense, he could go free. If he is ruled sane and found guilty of some or all the charges, he would be sentenced to prison time.
If he is not found to be mentally ill, prosecutors will ask for a prison sentence of 21 years, the maximum possible in Norway, a spokeswoman for the prosecutor's office has said.
Breivik has been held in Ila Prison since his detention after the killings.
Defense lawyer Geir Lippestad has previously said it is important to Breivik that people see him as sane so they don't dismiss his views.
During his trial, Breivik promised that he would not appeal if a court finds him sane and guilty. He is likely to appeal if he is acquitted on the grounds of insanity.
Breivik's rampage, the worst atrocity on Norwegian soil since World War II, prompted much soul-searching.
Norwegians reasserted their commitment to multiculturalism and tolerance at a series of mass public tributes held in the immediate aftermath of the massacre.
And earlier this month, Norway's chief of police stepped down after an independent commission detailed a catalog of police and intelligence failures.
It concluded that those errors cost police 30 minutes in getting to Utoya, and that dozens of lives might have been saved.
Speaking last month on the anniversary of the killings, Prime Minister Jens Stoltenberg urged Norwegians to "honor the dead by celebrating life," and said Breivik had failed in his attempt to change Norway's values.
CNN's Diana Magnay reported from Oslo and Laura Smith-Spark from London.
