PARIS — A Frenchman arrested over killings at a Belgian Jewish museum had traveled to Syria and claimed responsibility for the shootings in a video, prosecutors said Sunday.

Fears have been mounting in European countries that the hundreds of European radicals who are joining the fight in Syria against President Bashar Assad could stage attacks when they get home.

Police in the southeastern French city of Marseille arrested the suspect, Mehdi Nemmouche, on Friday after he arrived on a bus from Amsterdam, Paris Prosecutor Francois Molins told reporters. The suspect had an automatic weapon like that used in the Brussels attack, and ballistics analyses were under way to determine if it is the same weapon, Molins said.

The suspect’s was wrapped up in a white sheet scrawled with the name of the Islamic State of Iraq and the Levant, an extremist group fighting in Syria, Molins said. He said the suspect had spent about a year in Syria.

At a separate and nearly simultaneous news conference in Brussels, Belgian federal prosecutor Frederic Van Leeuw said the suspect had tried to film the killings on May 24, but his camera failed. A video found after his arrest shows his weapons and clothes, and includes his voice claiming responsibility for the attack, Van Leeuw said.

Belgian police carried out raids in case in the Courtrai region of Belgium on Sunday morning, where the suspect is believed to have spent time, and are questioning two people there, Van Leeuw said.

“The new elements in this investigation draw attention once more to the problem of the `returnees’ – in other words the people going to Syria to participate in combat and return afterward to our country,” he said. “All European countries are confronted at this moment with this problem.”

The Brussels killings, which came on the eve of European parliament elections in which far right parties had a strong showing, led Belgian officials to boost their anti-terror measures, and raised fears of rising anti-Semitism.

Two Israeli citizens and a French citizen were killed. A fourth victim remains hospitalized between life and death, the Belgian prosecutor said Sunday.

Video of the attack showed an athletic man with cap walking determinedly into the small Jewish Museum. The whole assault took a minute at most.

The suspect has been handed to anti-terrorist investigators and could be held at least through Tuesday under French counterterrorism law.

French President Francois Hollande promised Sunday to “fight” homegrown radicals who come home from Syria with violent plans.

Hundreds of people have left from France alone to fight in Syria’s 3-year-old civil war with Islamic extremists. The French government recently introduced new measures to try to stop disaffected youth from leaving in the first place, and better track those who go to Syria and come back.

Hollande said those efforts would be “amplified” in the coming months, without elaborating.

“The whole government is mobilized to follow the jihadists, and prevent them from being able to cause harm” especially when they come home to France or elsewhere in Europe, Hollande said on an official visit to Normandy.

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