A man armed with a bow and arrows went on a rampage in a Norwegian town outside Oslo on Wednesday, killing five people and wounding three others, in what the authorities said was an apparent act of terrorism.

In a statement, the police identified the suspect as 37-year-old Espen Andersen Brathen. The Norwegian security agency, known by its acronym, PST, said investigators were still trying to determine what motivated the attacker to carry out his grisly assault in the town of Kongsberg, about 50 miles southwest of Oslo.

The statement said Brathren had been apprehended in Kongsberg. Many flags across the normally bucolic town far from the bustle of the capital flew at half-staff, and grief-stricken residents placed candles and flowers at a makeshift memorial in the town square.

Earlier, the regional police chief said the suspect was known to the authorities.

“We have previously been in contact with him regarding worries about radicalisation,” Ole Bredrup Saeverud, the regional police chief, said at a news conference before the suspect was named.

Four women and one man were killed in the assault on Wednesday evening. The attacker, who escaped an initial confrontation with the police, unleashed a volley of arrows at apparent strangers in Kongsberg.

Officials said earlier Thursday that the assailant was a Danish citizen who lived in the town and who had converted to Islam.

The police chief said the last time concerns about the suspect’s radicalisation had been brought to the police’s attention was last year, but he did not say who had contacted them with those concerns.

Brathen is expected to appear before a judge on Friday, when the specific charges against him will be made public.

Fredrik Neumann, his court-appointed lawyer, said that the man was cooperating with the authorities and was undergoing a mental health evaluation.

The five people killed were aged 50 to 70, Bredrup Saeverud said, and the three people wounded in the attack were expected to survive.

It was the worst mass killing in Norway since 2011, when a far-right extremist killed 77 people, most of them teenagers at a camp.

On Thursday, the police offered new details about the attack. The first call to the police came at 6.12pm, with witnesses describing a scene of chaos and unprovoked violence at a supermarket in Kongsberg.

One woman told the local news outlet TV2 that she had seen people hiding from a man standing on a street corner with “arrows in a quiver on his shoulder and a bow in his hand.” As he shot the arrows, she said, people ran for their lives.

Six minutes after the first call, officers confronted the attacker. He fired arrows at the officers and escaped.

As he made his way through the town, he attacked people seemingly at random, according to the police. One of the injured was an off-duty police officer, and a photo of him with an arrow in his back was circulated widely online.

At 6.47pm, the police detained the suspect — 35 minutes after the first reports of violence.

A police lawyer, Ann Iren Svane Mathiassen, told TV2 that the suspect had lived in the town for several years.

Murder is rare in Norway. In a country with a population of just over five million, there were 31 murders last year.

Still, the nation has yet to fully reckon with the trauma of the devastating 2011 mass killing.

As the fallout from the latest attack reverberated, a new center-left government was being sworn in on Thursday morning.

Jonas Gahr Store, the Labour Party leader who was installed as Prime Minister, said at the ceremony that “what has happened in Kongsberg is terrible”.

He promised a full investigation.

New York Times News Service