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HELSINKI (AP) — Norway’s domestic intelligence agency says that such attacks as the one in the town of Kongsberg earlier this month are highly difficult to anticipate and prevent, and are likely to happen again in an open society such as Norway.

“This type of attack performed by a person on an impulse with simple means will happen again,” Arne Christian Haugstoeyl, counterterrorism chief at the agency known by the acronym PST, said in an interview with the Norwegian newspaper Aftenposten on Saturday. “I think it forces a discussion about what risk we must live with in a democratic and open society.”

Five people were killed and three others wounded in the southern Norwegian town of Kongsberg on Oct. 13 as the suspect Espen Andersen Braathen, a 37-year-old Danish citizen, attacked his victims with a bow and arrows and unspecified stabbing weapons.

How tragic the outcome will be in such cases in the future depends more on the police response time than on the degree to which an intelligence agency has managed to anticipate it, Haugstoeyl told Aftenposten. He added that “it’s not possible to guarantee that you can stop” an attack beforehand.

In 2017, PST notified Norwegian police that Andersen Braathen, who was on the agency’s radar, had released a threatening video.

“Unfortunately, there are many people who make hateful and threatening statements,” Haugstoeyl told Aftenposten. “Every week we get knowledge about an incredible number of videos, comments, photos and posts that are rougher and more extreme than this video.”

He was hesitant when asked by Aftenposten if PST could have done something differently to prevent the Kongsberg attack and said he would wait for the conclusions of an ongoing independent investigation into the police’s delay in capturing Andersen Braathen amid criticism that the response was too slow.

Andersen Braathen has confessed to the killings and has initially been charged with five murders. Norwegian police’s assessment is that the suspect’s apparent mental illness was the likely cause for the attack, while Andersen Braathen’s statement of being a convert to Islam had become a less important investigation line.

Police said on Monday that the rampage’s victims were likely stabbed to death after Andersen Braathen had first used arrows to wound them.