The Friday arrest of Mehdi Nemmouche, who allegedly murdered three people and left another brain-dead at the Jewish Museum in Brussels, marks the first time that a veteran of the Syrian jihad has come back to a Western country and put that struggle’s extremist ideology into action. But according to a former Israeli intelligence officer who has written extensively about the ripple effects of the jihad-influenced war in Syria, it will not be the last.

“Assuming that the initial reports are correct, this is not a surprise, said Col. (res) Reuven Erlich, the director of the Meir Amit Intelligence and Terror Information Center. “I see this as a sign of the future. It is a phenomenon that will endure and increase.”

Nemmouche, suspected of killing two Israelis and one Frenchwoman at the museum and mortally wounding a museum worker who is still hospitalized, was arrested Friday by French customs officials as he alighted from a bus that had traveled from Brussels to Marseille via Amsterdam. He was caught with a Kalashnikov assault rifle similar to the one used in the murder in Brussels and with a GoPro video camera like the one carried by the shooter.

Officials in the US, Europe and elsewhere have raised alarm bells of the possible risks posed by returning fighters, bolstering law enforcement efforts to crack down on possible jihadis.

Earlier this year, Erlich released a report warning that “the returning foreign fighters are a ticking time bomb, which can only be defused by international cooperation and joint systems to neutralize their terrorist-subversive potential.”

A picture released on June 1, 2014 shows the 29-year-old suspected gunman Mehdi Nemmouche. (photo credit: AFP PHOTO)

A picture released on June 1, 2014 shows the 29-year-old suspected gunman Mehdi Nemmouche. (photo credit: AFP PHOTO)

Belgian Interior Minister Joëlle Milquet was cited in the report as convening a December 2013 meeting of foreign ministers from Britain, France, Holland, Sweden, Spain, Australia, Canada and the United States in order to discuss “their influence on their countries of origin upon return.”

Erlich and the other researchers at the center, all veterans of the intelligence community in Israel, estimated that there were up to 2,100 Western fighters waging war in Syria, with Britain, France, and Belgium each providing hundreds of Islamist fighters. “The foreign fighters in the ranks of the Al-Nusra Front and Islamic State [of Iraq and Greater Syria] are a potential threat to international security,” the report stated. Some will return home and “continue their terrorist and subversive activities” on their own initiative; some “may be handled by al-Qaeda… exploiting the personal relationships formed in Syria”; and some, like the veterans of Afghanistan, may sow terror internationally, traveling with a Western passport, which raises fewer red flags.

Erlich said in a phone interview that while the 5,000 fighters from Arab countries make up the heart of the al-Qaeda-affiliated groups in Syria, the Western-based fighters, often second- and third-generation immigrants from Muslim lands, are quickly integrated into the fighting in the brutal civil war, with many spending less than a month in training and then roughly half a year in combat before circling back to their homes.

The European fighters return home inundated with Islamist ideology, intimately familiar with death and the weapons of war, and, he said, a ready-made potential network built around other returned fighters from the same European country.

Nemmouche, 29, is from Roubaix, the city in northern France where the al-Qaeda-influenced Gang de Roubaix was formed in the mid-nineties, noted IDC Herzliya senior researcher Ely Karmon. That terror group was formed around a French convert to Islam, Christophe Caze, a medical student, who traveled to Bosnia, became radicalized, and returned to France with the intent of committing murder.

People pay their respects in front of a makeshift memorial at the entrance of the Jewish Museum in Brussels, on May 25, 2014. photo credit: AFP/GEORGES GOBET)

People pay their respects in front of a makeshift memorial at the entrance of the Jewish Museum in Brussels, on May 25, 2014. photo credit: AFP/GEORGES GOBET)

In the immediate aftermath of the May 24 attack in Brussels, Karmon told The Times of Israel that he tended to doubt that Hezbollah was involved because Iran was unlikely to authorize a terror attack in Europe with the P5+1 nuclear talks moving into high gear, and because Hezbollah, were it to be implicated in such a high-profile strike, ran the risk of having not just its military wing outlawed in Europe – as happened in the aftermath of the 2012 attack in Burgas – but the entire organization.

“There are in Belgium, and in France, which is just three hours away, enough Salafist elements,” he said at the time.

Unwilling, however, to completely rule out Hezbollah involvement, he said Sunday that “the fact that the arrested guy was fighting in Syria in 2013 could lead to the possibility that he was recruited under a fake flag by Hezbollah,” much as was the case in a 2011 operation in which Hezbollah allegedly tried to subcontract the murder of the Saudi Arabian ambassador to the US to a Mexican drug cartel.