A woman lays a flower in front of the Jewish Museum of Brussels on May 25, 2014 where an attack by a lone gunman the day before killed two Israelis and a French woman. (Thierry Roge/AFP/Getty Images)

A suspected French jihadist who spent time in Syria is in custody over the shooting deaths of three people at a Belgian Jewish museum, prosecutors said Sunday, crystallizing fears that European radicals will parlay their experiences in Syria into terrorism back home.

When Mehdi Nemmouche was arrested Friday in southern France, he was in possession of firearms, a large quantity of ammunition and a video claiming responsibility for the May 24 attack, a Belgian prosecutor said.

In a one-minute rampage that shook Europe’s Jewish community, a gunman opened fire at the Brussels museum. In addition to the fatalities, one person was gravely wounded. Authorities raised anti-terrorism alert levels as they searched for the attacker.

Paris prosecutor François Molins said a customs inspection in the French port city of Marseille turned up Nemmouche as he disembarked from a bus arriving from Amsterdam.

The suspect had a revolver and a retractable automatic weapon like those used in the Brussels attack, and ballistics analyses were underway to determine whether they were used in the shooting, Molins said.

At least one of the weapons was wrapped in a white sheet bearing the name of the Islamic State of Iraq and Syria, an extremist group fighting in Syria, Molins said.

Nemmouche, a 29-year-old from northern France, has had seven convictions for crimes such as attempted robbery but nothing related to terrorism, Molins said.

He said the suspect became radicalized in prison and left for Syria three weeks after his last prison stay, in late 2012. Molins said Nemmouche had spent about a year in Syria, though it is unclear why he went and what he did there.

Belgian federal prosecutor Frederic Van Leeuw said in a news conference Sunday in Brussels that the suspect had tried to film the killings but that his camera failed.

A video found in his possession shows weapons and clothes and includes a voice-over asserting responsibility for the “attack in Brussels against Jews,” Van Leeuw said. He said it wasn’t certain whether the voice was that of the suspect.

“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,” Van Leeuw said. “All European countries are confronted at this moment with this problem.”

Interior ministers from European Union countries are expected to focus on strengthening ways to stem Syria-related violence when they meet Thursday in Brussels.

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

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

The attack and the arrest highlight the challenge for European authorities in tracking extremists — often alienated youths from immigrant backgrounds and with few job prospects — when they travel to and from Syria.

— Associated Press