Jakob Abdullahi Hassan (14) and Tone Ilebekk (48) were both stabbed to death on the premises of the Wilds Minne primary school 5th December 2016. Hassan was a student at nearby Fiskå school.
Hassan was stabbed 28 times and 48-year-old Tone Ilebekk 32 times in the 5th December 2016 murders.
Court proceedings have established that Ilebekk attempted to help Hassan, who was lying on a bench after being attacked, and thereafter became a victim herself.
At the time of his arrest, police described the then-15-year-old as part of the murdered 14-year-old's social circle, but said no connection was found between 15-year-old and Ilebekk, a mother of two and a worker at a nearby daycare centre.
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The accused appeared calm and smile as he entered the courtroom at Kristiansand District Court Monday, reports broadcaster NRK. He looked away and turned to his legal counsel to ask questions as relatives of the victims entered the courtroom, according to the report.
He also told the court that he had "hated Hassan for a long time" and linked the murder to a debt of 600 kroner ($71) that he claimed the 14-year-old owed him, NRK reported from the courtroom Monday.
One of the key questions for the court regarding sentencing will be whether the murder of Hassan was planned.
The maximum sentence the 16-year-old can receive is 15 years, since he is under the age of 18.
Police officers involved in the investigation of the crime are scheduled to give testimony during the first day of the trial.
Special investigating officer Cato Meijer and commanding officer Arivd Bjelkåsen of police security agency Kripos will be among the witnesses to be questioned in court.
The trial will be carried out behind closed doors, with only press and family of the victims present, due to the age of the accused, who recently passed his 16th birthday.
Proceedings are expected to take three days.