OSLO — The attacker who went on a rampage in a town in Norway killed his five victims using a “sharp object,” not a bow and arrow as had been widely reported, the Norwegian police announced on Monday.Espen Andersen Brathen, who confessed to the crime, did shoot arrows at people from a hunting bow during part of his attack last Wednesday in the town of Kongsberg, which also wounded at least three people.At some point in the rampage, the police said at a news conference Monday, he discarded the bow. The fatal blows are now said to have been delivered by a stabbing weapon or weapons, which the police did not identify. Four women and one man were killed in the attack about 50 miles southwest of Oslo.But it was the rarity of the other weapon used in the attack that caught the world’s attention, and if the hunting bow did not cause any deaths, it was responsible for at least one injury, that of an off-duty police officer who was struck by an arrow.One eyewitness, Rebecca Uttgard, 17, said she was in the town square Wednesday night near a shop owned by her mother and frequented by two of the people killed, when she heard warning shots fired by police officers responding to the scene.“I saw the arrows strewn on the ground,” Ms. Uttgard said. “I didn’t think, I just ran.”Friends and relatives of the victims said that a machete was also used in the attack.At the news conference, the police also addressed the shifting understanding of what prompted the attack.The police had previously contacted Mr. Brathen, a 37-year-old Danish citizen and Muslim convert, over concerns that he had been radicalized, and the Norwegian security agency, known as PST, said soon after the attack that it appeared to be an “act of terrorism.”But on Monday, Per Thomas Omholt, the chief of police in the Sor-Ost Police District, said of the motivation for the crime that “the initial hypothesis about conversion to Islam is weakened.”“He has said he converted in public, but he has not lived up to this in practice,” Mr. Omholt said.As part of the continuing investigation, the police have formally interviewed 60 people.“We are working to map the charged person’s background and motives, interview witnesses, maintain contact with the next of kin and victims, collect and analyze CCTV footage, conduct forensic examinations and examine electronic evidence,” Mr. Omholt said Monday.The attack rattled the quiet town Kongsberg, where violent crime is rare and the victims were apparently chosen at random.“It is difficult to swallow,” said Sturla Erstein, 55, a Kongsberg resident of 30 years. “I knew both the killer and one of the women who was killed.”Mr. Erstein said he had been particularly close with the victim, a ceramicist who sold him a cup around the corner from the memorial where he now places flowers. “I use that cup every day,” he said.The attack on Wednesday has prompted debates across Norway about how to deal with mentally unstable people who might pose a threat to others.“It’s the million-dollar question,” said Arne Christian Haugstoyl, the head of Norway’s counterterrorism unit at the Police Security Service. “I think there will be an important debate in Norway about what we can do about people who are severely mentally ill.”He said that attacks carried out by lone individuals or just a few people, and planned and executed in a short period of time, are one of the greatest threats to security in Norway.“This is not just a problem in Norway,” Mr. Haugstoyl said. “All security services all over the world, even the largest ones, struggle to stop this type of attack, because there are few preparations, not much communication, and little information for a security organization to monitor.’’Norway’s new prime minister, Jonas Gahr Store, who visited Kongsberg last week, said that “modern societies are vulnerable” to such attacks.“And in some ways we just have to live with vulnerability,” Mr. Store said in an interview with The New York Times. “Vulnerability comes from people falling out of community, and this is a phenomenon that we really need to study and address.”“We have to accept that you cannot find one response through a government decision that will eliminate vulnerability,” he said.