PARIS -- The French authorities announced Sunday that they had arrested a man in the killing of three people last month at the Jewish Museum in Brussels, identifying the suspect as a 29-year-old French man with a long criminal history who had traveled to Syria last year to join with radical Islamist fighters there.
The authorities said that they apprehended the man, identified as Mehdi Nemmouche, during a routine customs check Friday as he arrived by bus in Marseille from Brussels. They said he was carrying an assault rifle and revolver matching descriptions of those used in the deadly shootings May 24 at the museum in Brussels.
French and Belgian officials said there was evidence linking Mr. Nemmouche to the Islamic State of Iraq and the Levant, a jihadi group operating in Syria that until earlier this year maintained ties to al-Qaida.
European officials said the killings appear to be the first committed in Europe by a European citizen returning from the battlefields of Syria, a brand of violence that European officials have feared and warned against for months.
But it was not clear what help, if any, Mr. Nemmouche might have received from the Islamic State of Iraq and the Levant or any other group in allegedly planning and carrying out the attack in Belgium, or whether his motivation was linked to his time in Syria.
Officials in France were quick to stress the link. President Francois Hollande immediately praised the "effectiveness of our police forces" in preventing violence from the "jihadists" who have returned to France from Syria, saying the suspect in the Brussels killings had been stopped "as soon as he set foot in France."
But the case may yet raise questions about the ability of law enforcement and intelligence services to track potential suspects traveling to and from Syria. Mr. Nemmouche, who was found carrying a hat and shirt similar to one seen in the museum surveillance video of the shooting and a video taking credit for the attack, had been identified by the authorities as a potential jihadi at the completion of his last prison sentence in late 2012, but he was not placed under surveillance before departing for Syria shortly after his release.
Video cameras at the museum show a lone gunman pulling a Kalashnikov-type assault rifle from a bag May 24, firing it and then leaving on foot. Four people there were shot, three of whom died.
But his arrest is likely to intensify fears in Europe that European citizens returning from the battlefields of Syria may bring violence with them.
As many as 3,000 Europeans, including more than 700 French, are thought to have fought or to be fighting in Syria, most of them with the jihadi groups opposed to the government of Bashar Assad. France, with Europe's largest Muslim population and a deep pool of anger and resentment among the country's poor black and Arab youth, has already arrested dozens of men upon their return from Syria, charging some under the country's anti-terror laws and warning people thinking of traveling to Syria to join the conflict that their activities will be closely followed by the intelligence services.
Mr. Nemmouche was born in Roubaix, an impoverished industrial city in northeastern France near the border with Belgium.
He had been convicted seven times, on several occasions for driving without a license but also for violent robbery, and began a series of imprisonments in 2001, according to Francois Molins, the state prosecutor in Paris. Mr. Nemmouche appeared to have become radicalized during his time in prison; during his final stay, a five-year sentence, "he distinguished himself by his extremist proselytism," Mr. Molins told reporters Sunday, and fell in with other "radicalized Islamists."
Prison administrators "signaled" Mr. Nemmouche to the French intelligence services upon his release from prison, on Dec. 4, 2012, Mr. Molins said. Within about three weeks, however, Mr. Nemmouche had left France, bound for Brussels, London, Beirut, Istanbul and, ultimately, Syria, Mr. Molins said. French intelligence services believe it was there that he joined the Islamic State of Iraq and the Levant.
But they were unable to track him within Syria, Mr. Molins said. French intelligence learned March 18 of his departure from Syria, when German officials informed the French that he had arrived at Frankfurt Airport. After leaving Syria earlier this year, Mr. Nemmouche made what Mr. Molins described as an apparent effort to "cover his tracks," traveling to Istanbul, Malaysia, Singapore and Hong Kong, before returning to Europe via Frankfurt.
A video found in the suspect's possession shows weapons and clothes akin to the gunman's, and includes a voice claiming responsibility for the "attack in Brussels against Jews," Belgian federal prosecutor Frederic Van Leeuw said. He said it wasn't certain whether the voice was that of the suspect.
The narrator says he tried to film the killings live, but that his camera failed, Mr. Van Leeuw said. When apprehended, the suspect had a GoPro camera in his possession, the Belgian prosecutor said.
The Islamic State of Iraq and the Levant has made no public statement confirming or denying that Mr. Nemmouche was a member. Members of other Syrian rebel groups expressed frustration with the Islamic State of Iraq and the Levant and questioned the motives of foreign jihadis in Syria.
"I never heard of this jihadi in Brussels," said Maher al-Hamoud, a commander in the Syrian province of Hama for the Western-backed Free Syrian Army. "But people like these are delaying the victory in Syria."
Associated Press contributed.