The right-wing extremist Anders Behring Breivik, who killed 77 people in twin attacks in Norway last year, goes on trial in Oslo on Monday.
Since Breivik has already confessed to the deadliest attacks in Norway since World War II, the hearing will determine if he is to be sentenced to prison or a closed psychiatric ward.
A first court-ordered psychiatric exam found him insane, while a second opinion came to the opposite conclusion.
Breivik killed eight people when he set off a bomb in a van parked at the foot of government buildings in Oslo.
He then travelled to Utoeya island outside Oslo where, dressed as a police officer, he spent more than an hour methodically firing bullets at hundreds of people attending a Labour Party youth summer camp.
The shooting spree left 69 people dead, most of them teenagers.
Breivik has been charged with acts of terror.
The 33 year old has described his actions as cruel but necessary.