If the two experts determine that 32-year-old Anders Behring Breivik was sane and in control of his actions, the right-wing extremist risks a long prison sentence.
If not, he will be sentenced to psychiatric care.
The psychiatrists' report, which has been delayed by a month at their request, will be handed to the Oslo court at 9am, and the prosecutor's office is expected to reveal the main points at a press
conference at 1pm.
Behring Breivik is currently being detained in a high-security prison near Oslo. His trial is scheduled to open on April 16th, 2012 and last for about 10 weeks.
The maximum prison sentence for this type of crime under Norwegian law is 21 years, but Behring Brevik could stay behind bars longer if he is still considered a threat to society.
"I have a lot of questions. I'm very anxious to see what the report will be able to tell us," Behring Breivik's defence lawyer, Geir Lippestad, told Norwegian news agency NTB.
At the end of July, Lippestad said his client was probably "insane", an expression he later said he regretted, preferring instead to say he had "his own perception of reality."
On July 22nd, Behring Breivik first set off a car bomb outside the government buildings in Oslo that house the offices of Prime Minister Jens Stoltenberg, killing eight people.
After that, he went to the island of Utøya, some 40 kilometres northwest of Oslo, where, disguised as a police officer, he spent nearly an hour and a half methodically killing another 69 people, most of them teenagers.
Although he has confessed to the facts, Behring Breivik has refused to plead guilty, insisting his actions were "atrocious but necessary."
He has claimed to have been on a crusade against multiculturalism and the "Muslim invasion" of Europe.