A panel of judges will announce later whether they believe Anders Behring Breivik was criminally liable or insane when he killed 77 people in Norway last year.
They will deliver their verdict after 9am UK time and then explain their reasoning in a lengthy address to the court, which could take six hours.
The two professional judges and three lay judges presided over a 10-week trial in which harrowing testimony was heard from survivors of the day-long rampage.
The 33-year-old admits detonating a bomb outside the office of Prime Minister Jens Stoltenberg, killing eight people, and then driving to the island of Utoya where he shot dead 69 people at a Labour party summer camp.
As well as those who died, 242 were injured. The youngest victim was just 14 years old.
Breivik admits carrying out the attacks but says he was well aware of his actions, describing them as "cultural self-defence" to halt the "Islamisation" of Norway.
One of his defence lawyers, Vibeke Hein Bæra, says he has prepared two speeches to the court, for either judgement and will appeal the verdict, if he is deemed to be insane.
"I hope he will be given the right to make a few comments to the question of appeal or not - not to the verdict itself - but to why he wants to appeal."
She says he is likely to question the legitimacy of the court, but still accept a prison sentence.
The maximum tariff available to judges in the Norwegian legal system is 21 years, but further detention can be arranged if the inmate is still considered a risk to the public.
The verdict in the case is not considered legally binding until 14 days after it is delivered, to give either side time to appeal.
Whatever the outcome, Breivik will return to Ila prison on the outskirts of Oslo.
If he is found criminally liable and sentenced to "preventive detention" he will be confined to a suite of small cells in an area for prisoners considered to be "Particularly High Security".
Breivik would be the only person in that category in the entire country.
He would be limited to three rooms in a separate wing. In addition to sleeping quarters he would have his own exercise room and a study with a word processor.
Ellen Bjerke, the adviser to the prison governor told Sky News it is far from luxurious.
She said: "The other inmates have the entire prison at their disposal with gyms, libraries.
"They can go to work, they can go to school; there are all sorts of things going on. The prison is sort of like a mini society with all amenities.
"Those are not available to him."
If the judges decide he was insane on July 22, 2011, then he will receive treatment in a purpose-built ward also behind Ila's walls.
The possibility of appeals from either Breivik or the prosecution may prolong the uncertainty for the survivors and families of the victims.
An unedifying prospect for a country trying to forget the events of that day.