A 26-year-old man has turned himself into police, saying he was responsible for the knife attack that left three dead and eight wounded at a festival marking the German city of Solingen’s 650th anniversary, German authorities announced early Sunday.

Duesseldorf police said in a joint statement with the prosecutor’s office that the man “stated that he was responsible for the attack.”

“This person’s involvement in the crime is currently being intensively investigated,” the statement said.

Federal prosecutors said they were investigating the man on suspicion of murder, attempted murder and membership in a foreign terrorist organization. The suspect was to make a first appearance before a judge later Sunday.

The suspect is a Syrian citizen who had applied for asylum in Germany, police confirmed to The Associated Press. The dpa news agency reported, without citing a specific source, that his asylum claim had been denied and that he was to have been deported last year.

On Saturday, the Islamic State militant group claimed responsibility for the attack, without providing evidence. The terrorist group said on its news site that the attacker targeted Christians and that the perpetrator carried out the assaults Friday night “to avenge Muslims in Palestine and everywhere.” The claim couldn’t be independently verified.

Friday’s attack plunged the city of Solingen into shock and grief. A city of about 160,000 residents near the bigger cities of Cologne and Duesseldorf, Solingen was holding a “Festival of Diversity” to celebrate its anniversary.

People alerted police shortly after 9:30 p.m. local time Friday that a man had assaulted several people with a knife on the city’s central square, the Fronhof. The three people killed were two men aged 67 and 56 and a 56-year-old woman, authorities said. Police said the attacker appeared to have deliberately aimed for his victims’ throats.

The festival, which was due to have run through Sunday, was canceled as police looked for clues in the cordoned-off square. Instead, residents gathered to mourn the dead and injured, placing flowers and notes near the scene of the attack.

“Warum?” asked one sign placed amid candles and teddy bears. Why?

Among those asking themselves the question was 62-year-old Cord Boetther, a merchant from Solingen. “Why does something like this have to be done? It’s incomprehensible and it hurts,” Boetther said.

Officials had earlier said a 15-year-old boy was arrested on suspicion he knew about the planned attack and failed to inform authorities, but that he was not the attacker. Two female witnesses told police they overheard the boy and an unknown person before the attack speaking about intentions that corresponded to the bloodshed, officials said.

The attack comes amid debate over immigration ahead of regional elections next Sunday in Germany’s Saxony and Thueringia regions, where anti-immigration parties such as the populist Alternative for Germany are expected to do well. In June, Chancellor Olaf Scholz vowed that the country would start deporting criminals from Afghanistan and Syria again after a knife attack by an Afghan immigrant left one police officer dead and four more people injured.

The IS terrorist group declared its caliphate in large parts of Iraq and Syria about a decade ago, but now holds no control over any land and has lost many prominent leaders. The group is mostly out of global news headlines.

Still, it continues to recruit members and claim responsibility for deadly attacks around the world, including lethal operations in Iran and Russia earlier this year that killed dozens of people. Its sleeper cells in Syria and Iraq still carry out attacks on government forces in both countries as well as U.S.-backed Syrian fighters.