PARIS (AP) — Investigators working to understand why a 20-year-old French citizen born in the Russian republic of Chechnya went on a stabbing rampage in central Paris detained the dead suspect’s parents and a friend Sunday, French officials said.

Counterterrorism investigators want to know if the assailant, identified by Chechnya’s leader as Khamzat Azimov, had help or co-conspirators. The attacker killed a 29-year-old man and wounded four other people with a knife before police fatally shot him Saturday night.

The suspect was on a police watchlist for radicalism, a judicial official not authorized to speak publicly about the case told The Associated Press. But he had a clean criminal record and did not know his victims, Interior Ministry spokesman Frederic de Lanouvelle said.

The parents were detained in Paris’ northern 18th district and the friend was detained in the eastern French city of Strasbourg on Sunday afternoon, the judicial official said.

French media reported Sunday that Azimov had lived in Strasbourg, which is 492 kilometers (306 miles) from Paris. It was unclear if he was residing with his parents in the French capital when he carried out the attack.

Witnesses reported hearing the man shouting “Allahu akbar,” the Arabic phrase for “God is great,” during the attack that happened at about 9 p.m. in a lively area near the Opera Garnier.

The Islamic State group claimed the attacker was one of its “soldiers” three hours later, but provided no evidence to back the claim or details about his identity.

The assailant was listed in a nationwide database of thousands of people suspected of links to radicalism, according to the judicial official. Extremists behind multiple attacks in France in recent years have turned out to be on the watchlist.

‘Allahu Akbar’ Paris Knife Killer Was Radical Muslim Migrant on Jihadist Watch List https://t.co/RF81RcREzo — Breitbart London (@BreitbartLondon) May 13, 2018

The official said the suspect was born in November 1997 in the largely Muslim Russian republic of Chechnya, where extremism has long simmered.

Chechnya’s president insisted Sunday that France bears responsibility for the knifings, pointing out that Azimov only held a Russian passport until he was 14-years-old.

“I consider it necessary to state that all responsibility for the fact that Khazmat Azimov went on the road of crime lies completely with the authorities of France,” Chechen President Ramzan Kadyrov said. “He was only born in Chechnya, and his growing up, the formation of his personality, his views and persuasions occurred in French society.”

The attacker targeted five people and then fled, according to Paris police and a witness. When police officers arrived minutes later, he threatened them and was shot dead, police union official Yvan Assioma said. Several witnesses said the attacker ran directly toward police.

Bar patrons and opera-goers described surprise and confusion, and being ordered to stay inside while the police operation was underway on rue Monsigny in the lively 2nd arrondissement, or district, of the French capital.

“I was working in the restaurant and suddenly I heard a woman screaming … he came and attacked her,” Jonathan, a witness working nearby who wouldn’t provide his last name, recalled. “That’s when the panic started. Everyone started screaming and trying to reach our restaurant. … The attacker just kept walking around with his knife in his bloodied hands.”

“Police were quickly on the scene, in less than five minutes. They encircled him and he tried to attack them with a knife but they shot him down,” he told reporters.

A 23-year-old Brazilian tourist from Washington told The Associated Press that she and her aunt saw the fatally wounded victim on the ground and watched the ambulance arrive and rescue workers try to revive him.

“They kept doing CPR for what seemed to be a really long time and, in the end, he passed, and they put the sheet over him,” Carolina Melo said. She said she and her aunt had been in their hotel, went out to investigate the noisy confusion nearby but retreated after hearing several shots of gunfire. The scene, she said, “was kind of a mess.”

A police official said the assailant didn’t have identity documents with him during Saturday’s attack but was identified thanks to DNA.

Among the injured was a 34-year-old man from Luxembourg, the foreign ministry of the small country north of France said in a statement. The four people injured are out of life-threatening danger, French Interior Minister Gerard Collomb said.

Collomb held a special security meeting Sunday to address the Paris attack.

U.S. Secretary of State Mike Pompeo said the United States would lend a hand in the investigation.

“The French authorities with all the intelligence help the United States can provide will do our best to unpack this in the coming hours,” Pompeo said Sunday on Fox News.

The Islamic State group’s Aamaq news agency said the assailant acted in response to the group’s calls for supporters to target members of the U.S.-led anti-IS military coalition. France’s military has been active in the coalition since 2014, and IS adherents have killed more than 200 people in France in recent years.

The Russian Embassy in France said it has requested more information on the attack suspect. Some refugees fleeing wars in Chechnya in the 1990s and early 2000s settled in France, but Chechens have not been responsible for past high-profile attacks in the country.

Two Chechen brothers were behind the deadly bombing of the Boston Marathon in 2013.