Until now, the trail of Islamist terrorism seemed privileged.
And then the first elements of the psychiatric expertise sowed the seeds of doubt.
Two days after the archery attack that killed five in Norway, the thesis of the killer's mental illness is now gaining momentum at this stage of the investigation, Norwegian police said on Friday.
"The hypothesis that was most reinforced after the first days of the investigation is that of (mental) illness as a backdrop," Inspector Per Thomas Omholt said at a press conference.
"But we are leaving the door open to other hypotheses."
Among the theories considered, the police had listed "anger, revenge, an impulse, jihad, disease and provocation".
These statements reinforce the doubts surrounding the mental health, and therefore the criminal responsibility, of Espen Andersen Bråthen, who admitted to having killed five people and having injured three others, Wednesday in Kongsberg (south-eastern Norway), where he resides.
Suspected of Islamist radicalization, this 37-year-old Dane was placed in pre-trial detention for four weeks on Friday, the first two in total isolation.
Rather than in prison, he will be kept in a medical institution, said prosecutor Ann Iren Svane Mathiassen.
Transferred to a psychiatric facility
Mr Bråthen was transferred Thursday evening to a mental institution following "an assessment of his state of health". He is undergoing a psychiatric assessment by experts to determine whether he can be held criminally responsible for his actions. The conclusions are expected to take several months.
If the attacks bear, they say, the mark of a "terrorist act", the authorities now seem to lean towards the hypothesis of madness.
"There is no doubt that the act itself apparently suggests that it may be a terrorist act, but it is now important that the investigation progress and that the motivations of the suspect, ”said the head of the internal security services (PST), Hans Sverre Sjøvold, on Thursday.
"He's a person who has been going back and forth through the health care system for a while."
Previously reported for radicalization, Mr. Bråthen converted to Islam a few years ago.
According to Norwegian media, the PST, the counterterrorism service in Norway, warned in 2018 that the suspect could commit "a small-scale attack".
Archery attack in Norway: suspect is radicalized Dane
The suspect was also reportedly targeted by two court rulings in the past: a ban last year from visiting his parents, after threatening to kill his father, and a conviction for burglary and buying hash in 2012.
Mr Bråthen, who probably acted alone according to the police, killed four women and a man aged between 50 and 70 years old in several places in Kongsberg, a small town without history of about 25,000 inhabitants, some 80 km to the west of Oslo.
The country has also been bereaved by two far-right attacks in the past decade, including the one by Anders Behring Breivik on July 22, 2011, which left 77 people dead.