German police are hunting for a man who on Friday night attacked nearly a dozen people with a knife, killing three, during a street festival in the western city of Solingen.

At a news conference on Saturday afternoon, the authorities said they had not ruled out that it was a terrorist attack because no other explanation for the seemingly random violence made sense.

The police said they had detained a 15-year-old boy for questioning whom they believed might have had prior knowledge of the attack. The state attorney is not treating the youth as a suspect.

What happened?

Shortly after 9:30 p.m., the attacker started stabbing people who had gathered at the festival to celebrate Solingen’s 650th anniversary. The attack occurred during a live music performance, not far from a temporary stage set up for the event, which was billed as a “Festival of Diversity.”

The police said it appeared that the attacker chose victims from the crowd at random and that he appeared to target at least one of the victims’ necks.

The festival, which was planned to run through Sunday, was immediately canceled as emergency workers tended to the injured and the police tried to get a handle on the situation.

Besides the three people who died of their injuries, another eight were injured. Of those, four remain in critical condition.

The police have interviewed witnesses and survivors to try to reconstruct the attack and have asked the public to upload any videos or pictures of the event to the official tip site of the state police.

Early Saturday morning, the police raided the house of the 15-year-old boy, whom several witnesses say they overheard communicating with the suspect before the attack took place. The public prosecutor said the boy was being investigated for not reporting a crime.

What’s next?

“Our authorities are doing everything they can to catch the perpetrator and to determine the background of the attack,” Nancy Faeser, Germany’s interior minister, said in a statement on Saturday. Officers from neighboring areas have been brought in to try to help the local police find the attacker.

The police have so far declined to make public any details about the man.

“The perpetrator must be caught quickly and punished with the full force of the law,” Chancellor Olaf Scholz said in a statement posted to his X account on Saturday.

Two nearby towns have also canceled public festivals that they had planned for the weekend. “We cannot celebrate when our neighboring city is mourning just a few kilometers away,” said Bettina Warnecke, the mayor of Haan, which canceled its wine festival. In comments reported by the D.P.A., a German news service, Ms. Warnecke noted that security was also an issue, given that the police had not found the man they believed to be the attacker.

What are some key facts about Solingen?

Solingen, home to more than 150,000 people, is just east of Düsseldorf, the capital of Germany’s most populous state, North Rhine-Westphalia.

Known around the world for the production of high-end knives and scissors, Solingen calls itself the “city of blades.” The attack happened in the busy square at the heart of the festival celebrating the 650th anniversary of the first written mention of the city.

Solingen is a diverse city that has benefited from foreign workers since the guest worker programs of the 1960s brought foreign workers to the city’s many blade manufacturers. More than 20 percent of the city’s residents are not German citizens, and thousands more hold dual citizenship.

The city was the site of one of the most traumatizing racist attacks in postwar Germany, in 1993, when a group of young neo-Nazis set fire to a house inhabited by a Turkish family. Five people were killed, including three children, and 17 people were injured.