Several clues led police to the boy, who confessed almost immediately after being questioned by officers on Tuesday night. He has given a detailed statement to the police, who say that they have no reason to question his account.

“We have no concrete evidence that there was more than one perpetrator,” police spokesman Terje Kaddeberg Skaar said at a press conference Wednesday morning.

Jakob Abdullahi Hassan (14) and Tone Ilebekk (48) were both stabbed to death on the premises of the Wilds Minne primary school on Monday afternoon. Hassan was a student at nearby Fiskå school.

Police described the arrested 15-year-old as part of the murdered 14-year-old’s social circle but said no connection has been found between 15-year-old and Ilebekk, a mother of two and a worker at a nearby daycare centre.

Police would not say on Wednesday morning if the teen offered a motivation for his actions.

“The accused has given an explanation that is detailed, and I’m not going to share that explanation with the public. It is important for the police that it not be disclosed,” Skaar said.

The boy is currently under the watch of mental health professionals and will be produced for remand later on Wednesday.

“This was already a tragic case. It is no less tragic when a 15-year-old boy is behind it,” Skaar said.

Police said the 15-year-old has not been registered with the police before, but nothing was said about his upbringing or where in Kristiansand he lives.

“Now there is also an additional family that is powerfully affected by this tragic event,” Skaar said.

The families of both victims were informed of the guilty plea on Tuesday night and are be attended by emergency personnel.Police said that they were led to the boy by tip-offs from the public.

“The charges are the result of an intensive investigation that took part in the initial 30 hours. All the tips we have received from the public have been helpful for us and are part of the picture that led to this,” Skaar said.

Police said they would not go into detail about the stabbing or the weapon that was used. Although the 15-year-old has confessed, police will continue an intensive investigation of the double murder.

The Wilds Minne School houses first through seventh graders as well as a large after-school programme. According to a school official, no students there witnessed the fatal stabbings