A judge in Norway will rule in a custody hearing on Friday for the man who confessed to a deadly bow-and-arrow attack that police have said was probably an act of terror.

Emotions were still running high in Kongsberg, a quiet town in southeastern Norway, where residents gathered on Thursday evening for a candlelit vigil 24 hours after the attack that left five dead and three injured.

"We're a small community and we need to be there for each other," Kristine Johansen, a 29-year-old teacher, told AFP.

Kongsberg
Kongsberg, a quiet town in southeastern Norway, was let shaken by the bow-and-arrows attack Photo: NTB / Terje Bendiksby

Police have described Espen Andersen Brathen as a 37-year-old Danish citizen who converted to Islam and is believed to have been radicalised.

He has confessed to killing five people and injuring three on Wednesday in Kongsberg, using a bow and arrows and other undisclosed weapons before police managed to arrest him.

"We would like to have him in custody for at least four weeks," prosecutor Ann Iren Svane Mathiassen told AFP.

Kongsberg
Police in southeastern Norway are investigating and questioning witnesses after a man armed with a bow and arrows killed five people Photo: AFPTV / Viken KANTARCI

The Kongsberg court was expected to make its decision without Brathen being present.

"I think he will probably not show up," Svane Mathiassen said, adding that Brathen had not contested the detention request.

Investigators appeared to be treating the case as an act of terror given the nature of the attack with rudimentary weapons, the fact that he attacked his victims randomly and that red flags had been raised about his possible radicalisation.

"There is no doubt that the actual act appears as if it could be an act of terror, but it's important that the investigation continues and that we establish the motive of the suspect," the head of Norway's intelligence service PST, Hans Sverre Sjovold, told a news conference on Thursday.

Kongsberg terror attak
Investigators appeared to be treating the case as an act of terror given the nature of the attack Photo: NTB / Terje Bendiksby

Authorities have however not ruled out the possibility of mental health illness.

"This is a person who has been in and out of the health system for some time," Sjovold said.

According to Svane Mathiassen, a psychiatric evaluation of Brathen began on Thursday.

Kongsberg terror attack
The attacker killed four women and a man, aged between 50 and 70, in several locations in Kongsberg Photo: NTB / Terje Pedersen

"It could take maybe a couple of months" before the evaluation is completed, she said.

The suspect was known to PST, which is in charge of Norway's anti-terrorism efforts, but few details have emerged about why.

"There were fears linked to radicalisation previously," police official Ole Bredrup Saeverud told reporters.

Those reports were before this year, and police had followed up at the time.

Norwegian media reported that Brathen was subject to two prior court rulings, including a restraining order against him regarding two close family members after threatening to kill one of them, and a conviction for burglary and purchasing narcotics in 2012.

Local media also unearthed a video Brathen allegedly posted to social media in 2017, in which he issued a "warning" and declared his Muslim faith.

Brathen is believed to have acted alone when he killed four women and a man, aged between 50 and 70, in several locations in Kongsberg where he lived.

The picturesque, tranquil town of 25,000 people is located about 80 kilometres (50 miles) west of Oslo.

Speaking anonymously, one of Brathen's neighbours described the suspect as a big person with a crew cut and a serious demeanour, who was always seen "alone".

"No smile, nothing in the face. He was just staring," the neighbour told AFP.

Several planned jihadist attacks have been foiled by security services.

Copyright AFP. All rights reserved.