BRUSSELS — More than half the Europeans who joined ISIS in Syria and Iraq had criminal backgrounds unrelated to terrorist activities, according to an academic research group that studies international security issues.



The study by Globsec, a Slovakian research firm, confirms what has long been suspected — that prison is a convenient recruiting zone for radical groups seeking new adherents. The concern is so powerful among French authorities that in February of this year, the French prison system began a program to isolate as many as 1,500 or more prisoners considered a danger to spread radical ideology to other inmates.

“Our prisons have done more to recruit terrorists than any online video or program,” said one French counterterrorism police officer who works undercover and cannot be identified.

The report also concluded that the average age of a Europe-based ISIS fighter was 30, older than many expected. More than 70% were either born in Europe or hold permanent EU residency, a refutation of the oft-stated view of European rightists that refugees use Europe as a base for terrorism.

The report, which was paid for by a grant from Phillip Morris, the tobacco conglomerate, found that the impact of prison on whether someone might become radicalized varies widely by country.

“Of the five biggest subsets in the dataset, the French one is 50% composed of former criminals, and the UK’s is 32%, but the Spanish one is only 6.4% and the Italian, 7.4%,” the study concluded. Those numbers might also reflect the much smaller presence in ISIS of fighters from Italy and Spain — estimated in the hundreds versus the thousands of French and British citizens known to have joined ISIS.

The study focused on 197 of what it described as "jihadi terrorists" and 28 nationalist or leftist terrorists, primarily from Greece. Even those cases, however, showed a link between prison time and subsequent terrorist activity — in the case of the Greek suspects, none of whom were tied to Islamic extremism, 43% had served time in prison.

The study also found that in contrast to al-Qaeda, ISIS members from Europe were significantly less educated and had spottier employment records: Only 20% of the ISIS recruits studied had attended high school, and only 3% had completed undergraduate studies, the report concludes. For those who had spent time in prison before joining ISIS, the number was even lower: Just 8% had attended high school.

Forty percent of the 197 terrorist suspects studied were unemployed when they were arrested or killed, the study found.