A suspect in the May 24 shooting in the Jewish Museum in Brussels that left four dead has been detained, sources involved in the police probe of the attack said Sunday.

The alleged culprit, 29-year-old French citizen Mehdi Nemmouche from the northern French town of Roubaix, was captured Friday in Marseille, and was said to have in his possession a gun and a Kalashnikov assault rifle of the sort used in the May 24 attack.

Belgian investigators are probing a possible terrorist link, noting Nemmouche is believed to have links to Syrian jihadists. Nemmouche last visited Syria in 2013.

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While Belgian authorities have officially said that the attack on the museum was most likely a racially motivated hate crime, the authorities began earlier last week to probe possible terror connections.

Federal prosecution spokeswoman Wenke Roggen said the fact that the attack lasted only a minute and a half has led authorities to believe there could be a terrorist motive. Deputy public prosecutor Ine Van Wymersch added that the identity of the two Israeli victims also figured heavily into the assessment.

The Israeli victims, Mira and Emmanuel Riva, a couple in their 50s, had worked for the Israeli government in the past, though only in administrative and accounting capacities, as far as is known.

Originally from Roubaix in northern France, Nemmouche is believed to have traveled to join Islamist fighters in Syria in 2013, and was known to the French domestic intelligence agency DGSI, the source said.

He is being questioned by the DGSI, which can hold him for up to 96 hours, until Tuesday, or 144 hours, to Thursday, if investigators invoke an imminent terrorist threat.

Sources close to the investigation told AFP that during the first 24 hours of interrogation, Nemmouche remained silent.

Nemmouche was convicted and sentenced to two years in prison for a robbery in a small supermarket in the northern town of Tourcoing in August 2006, his lawyer Soulifa Badaoui said.

She said he had at the time denied any involvement and added that a subsequent raid in his house yielded no incriminating evidence.

President Francois Hollande said Sunday that the suspect was “arrested as soon as he set foot in France.”

“The government is mobilized to track down jihadists and prevent them from causing more harm,” he said, adding that the action plan to fight them will “be strengthened in the coming months.”

According to the latest figures, some 780 people have left France to fight with jihadists in Syria.

All four victims of the shooting, who included a French woman who did volunteer work at the museum and a 24-year-old Belgian museum employee, were hit by bullets to the face and neck.

The young Belgian was said by Jewish leaders to have died last Sunday of injuries sustained in the shooting, but Van Wymersch said he was still alive but “clinically dead.”

Three chilling security camera videos show the gunman, wearing a cap and sunglasses, but with his features hard to make out, walk into the museum entrance, remove a Kalashnikov-style automatic rifle from a bag and then shoot through a door before making an exit.

The museum in the heart of Brussels has been closed as investigators continue their inquiry.

The attack was the first such incident in more than 30 years in Belgium and has revived fears of a return of violent anti-Semitism to Europe.

Some 40,000 Jews live in Belgium, roughly half in Brussels and the remainder in the port city of Antwerp.

The profile of Nemmouche also stands to revive a row in France over the monitoring of those who leave to country to fight in Syria.

France unveiled plans in April to try to stop the increasing numbers of young French Muslims heading to fight in Syria’s civil war and becoming radicalised before returning home.

Times of Israel staff and AP contributed to this report.