Quilliam MD Ghaffar Hussain writes for The Daily Beast about the implications of the Mehdi Nemmouche arrest in connection with the Belgian Jewish Museum attacks in May.

It is a scenario that counter-terrorism experts have been warning about for the past two years: a European citizen who travelled to Syria in order to join up with jihadist groups returns to Europe in order to carry out a terrorist attack. It is something we all knew eventually would become a reality and, more worryingly, knew we could not prevent.

On May 24, a lone gunman opened fire at the Jewish Museum of Belgium in Brussels, killing an Israeli couple and a French woman before escaping. On May 30, a 29-year old French national by the name of Mehdi Nemmouche was arrested getting off a bus in Marseille after a routine customs search found guns and ammunition in his luggage. They were of the same kind used in the shooting—and with them, reportedly, was a 40-second video claiming responsibility.

It turns out that Nemmouche had travelled previously to Syria and fought alongside the Islamic State of Iraq and the Levant (abbreviated to ISIL or ISIS) before returning to his native France. Prior to his Syria trip he served time in a French prison for armed robbery, among other offenses. It was during his stint in prison that he is believed to have become radicalized and there have been reports that he proselytized extremist ideology while he was incarcerated.

Nemmouche has not been convicted of the Jewish Museum shooting yet, but the evidence pointing in his direction, thus far, is fairly damning. Already, debates about “lone wolf” terrorists, prison radicalization and European-Syrian foreign fighters have been revived. The target, a Jewish Museum, should not come as any surprise either, since anti-Semitism is a central part of jihadist ideology.

Quilliam recently published a report on online extremism, “Jihad Trending” (PDF), which debunked the lone wolf phenomenon and the potential for prison radicalization, especially in France. We found that even in cases where individuals acted alone, in an operational sense, they were not radicalized in a vacuum.

In France, Muslims represent an estimated 8 percent of the population, but make up about 53 percent of the prison population. It has been reported in the past that around 150 French prisoners have been caught promoting extremist ideology, while at the same time it is difficult for mainstream imams and mentors to gain access to the French Muslim prison population.

Khaled Kelkal, who was involved in the 1995 bombings in France, and Mohammad Merah, who went on an ideologically motivated shooting spree in 2012, both served time in French prisons for criminal activity and went on to commit terrorist acts.

Nemmouche is one of an estimated 700 French nationals to have travelled to Syria in order to fight on the side of jihadist groups operating there. In his case, he appears to have joined a jihadist faction, ISIS, so extreme that even al-Qaeda has disavowed it. Similarly, an estimated 400 British citizens have travelled to Syria in order to join jihadist groups, while Dutch, Danish, German and Belgian nationals also are believed to have made the trip.

Given that previous European terrorists travelled to Afghanistan and Pakistan (among them Merah and Muhammad Siddique Khan, the mastermind of the July 2005 bombings in London), the fear that these European foreign fighters would return to wreak havoc on European soil has been palpable in the media and in political circles. In Britain, the police have been working hard to involve family members of itinerant jihadists in dissuasion programs. But in the public domain there have been few counter-narratives persuading individuals not to go to Syria in the first place, thus allowing extremists to monopolize the debate.

Regardless of whether or not Nemmouche is convicted for the Brussels shootings, Syrian foreign fighters do pose a clear threat to Europe. As such, a much more coherent strategy to contain and prevent this menace needs to be developed and articulated:

Support needs to be offered to those who can develop convincing counter-narratives, and the glamour that surrounds fighting in Syria needs to be removed.

Prisons on both sides of the English Channel need to invest in de-radicalization programs and offer quality mentoring to those at risk.

The security services also need to have a plan of action for those returning from Syria that involves assessing the threat they pose, and those that are a potential threat need to be kept under surveillance.

With Syria, Libya, Afghanistan, Somalia, Iraq and Nigeria in the grip of jihadist insurgencies, and with Muslim communities in Europe over-represented in prison populations and often feeling at the fringes of society, the potential for Islamist radicalization remains very real. It is no longer hypothetical. It is an issue we need to get to grips with as soon as possible, before more innocent blood is spilled on Europe’s streets.

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