"The theory that [the crime] is rooted in some kind of Illness is becoming more and more valid ... The final conclusion will be made after psychological examination," police spokesman Per Thomas Omholt said during a press conference.
According to the police officer, the perpetrator was hospitalised.
"His health is such that it was necessary to send him to a medical facility. He is not in prison, but in a secure medical facility," Omholt added.
On Wednesday evening, the police arrested a man in Kongsberg who shot arrows at people, killing five and wounding several more. The archer is a 37-year-old Dane living locally, who admitted to his crimes and is willing to cooperate with the investigation.