STRASBOURG, France (AP) — French police conducted an intense but ultimately fruitless search Thursday in the Strasbourg neighborhood where a suspected gunman who killed three people and wounded 13 near a popular Christmas market was last seen.

Security forces, including the elite Raid squad, took action in the Neudorf neighborhood based on "supposition only" that 29-year-old suspect Cherif Chekatt could have been hiding in a building nearby two days after the attack, a French police official said. Chekatt grew up in Neudorf, just south of the city center.

The official, who could not be identified because he was not authorized to disclose details of the investigation, said reports of a person seen moving through gardens prompted police to response, but they did not turn up anything after about two hours.

Chekatt allegedly shouted "God is great!" in Arabic and sprayed gunfire from a security zone near the Christmas market Tuesday evening. Authorities said he was wounded during an exchange of fire with security forces and a taxi driver dropped him off in Neudorf after he escaped.

French Interior Minister Christophe Castaner said the operation was aimed at "removing doubts" and didn't mean the suspect necessarily was in the Neudorf area. Police have executed several similar maneuvers since Tuesday's attack, Castaner said.

Prosecutors have opened a terror investigation. More than 700 officers have been searching for the suspect, who had a long criminal record and had been flagged for extremism, government spokesman Benjamin Griveaux told CNews television.

Asked about the instructions they received, Griveaux said the focus was catching Chekatt "as soon as possible," dead or alive, and to "put an end to the manhunt."

So far, five people have been arrested and remanded in custody in connection with the investigation, including Chekatt's parents and two of his brothers.

The Paris prosecutor's office said the fifth, who was arrested Thursday at an undisclosed location, was a member of Chekatt's "entourage" but not a family member.

Police distributed a photo of Chekatt, with the warning: "Individual dangerous, above all do not intervene."

France has raised its three-stage threat index to the highest level since the attack and deployed 1,800 additional soldiers across the country to help patrol streets and secure crowded events.

In the wake of the attack, Griveaux called on protesters who have become known as the "yellow vests" and who have been demonstrating across France since last month not to take to the streets again this weekend.

French authorities said Chekatt, born in Strasbourg, appeared on a watch list of people flagged for extremist views. They said he had 27 criminal convictions, receiving the first at age 13.

The people who died in the attack included a Thai tourist, 45-year-old Anupong Suebsamarn, according to the Thai Foreign Ministry. Five of the wounded were in serious condition, the prefecture of the Strasbourg region said.

French President Emmanuel Macron was in Brussels on Thursday for a European Union summit. EU leaders held a minute of silence for the latest victims of a mass shooting in France.

Hundreds of people gathered in Strasbourg's 500-year-old cathedral Thursday evening to mourn and seek comfort.

"Evil does not prevail," Archbishop Luc Ravel said. "And the message of Christmas has not been contradicted but rather confirmed by Tuesday's dramatic night: Evil and good are both there, but in the end the good will have last word."

Strasbourg's usually busy streets were eerily empty Thursday morning, with a heavy police and military presence. Some lit candles and brought flowers to a makeshift memorial at the site of the attack.

"You can feel a very heavy atmosphere due all these events," said resident Lucille Romance. "People are in a state of shock and are avoiding getting out of their house."