The fact that most of the Paris attackers identified so far were European-born radicals has once again shined the spotlight on the growing problem in the West of homegrown extremism.
Authorities have identified four Frenchmen and two Belgians as suspects in the shootings and suicide bombings that killed 129 people on Friday. That puts them among ISIS's legion of foreign fighters, estimated by the CIA to number over 20,000.
A seventh suspect's body was found near a Syrian passport, but its authenticity has come under scrutiny after Serbian police arrested a man with an almost identical copy, the Guardian newspaper reported.
The European backgrounds of the perpetrators puts France and the West in the difficult position of trying to understand why their own citizens would sacrifice their lives to murder their neighbours on behalf of an extremist organization in another part of the world — a question radicalization analysts say is almost impossible to answer.
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There is no reliable profile for many of the candidates being recruited by extremist Islamic groups, Phil Gurski, a former intelligence analyst with the Canadian Security Intelligence Service, told CBC News.
"Throughout my career at CSIS and looking at a lot of these things, we simply found that there were no useful elements in terms of profiles, whether it was age or ethnicity or employment status or education or psychological or criminal background," Gurski said.
Abdelhamid Abaaoud, the suspected mastermind of the Paris attacks, killed in a police assault, was a lifelong Muslim and the child of Moroccan immigrants.
By contrast, Damian Clairmont, the Calgary man who died fighting with ISIS in Syria last year, was a white Muslim convert with an Acadian ancestry.
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Even gender is not a guaranteed common factor, as there have been multiple reports of Canadian women joining ISIS.
"We've had people — poor, rich, married, unmarried, mental illness, converts, not-converts — and so there's nothing really there in terms of profile," says Amarnath Amarasingam, a post-doctoral fellow who researches terrorism and radicalization at Halifax's Dalhousie University.
"What all of them do tend to have in common ... is youth, [with a] thrust towards meaning and purpose and significance. A lot of these youth don't feel like they fit into the broader society, they don't feel like they belong."
Giving ISIS what they want
The fact that ISIS preys on those who feel isolated and excluded should be a wake-up call for Western nations to build more inclusive societies, says Rima Berns-McGown, a University of Toronto history professor who researches how government policy affects youth radicalization.
She's concerned that certain state responses to the Paris attacks, like closing doors to Syrian refugees, play into ISIS's hands.
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"The reason ISIS does these things, launches these attacks and so on, is because it actually wants to create an environment in which the West appears to be hostile to people who are not of the West. It wants to create a sort of civilizational war," she said.
"It wants to create anger and resentment. It wants to create Islamophobia. It wants to create racism. Because if it does that, it makes the lives of individual Muslims more uncomfortable, and it wants to say, 'You cannot be at home in the West. You need to come and be at home in the only place that will respect you.'"
For his part, Amarasingam said ISIS is unique among Islamic extremists organizations in selling this "utopian" vision of a caliphate, or Islamic state, where people can find a sense of belonging.
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"It's a state where they believe that Islamic law is being practiced in its purest and fullest form, and therefore all Muslims around the world have an obligation to make migration to that state," he said.
"The fact that the vast majority of Muslims around the world disagree that this is the authentic Islamic state doesn't seem to bother them too much." But many of the youth it is able to recruit "are drawn to that nation-building, utopian vision that they're portraying themselves to be."
The warning signs
When people start to buy into this propaganda, they exhibit certain behaviours.
In his book The Threat From Within: Recognizing al-Qaeda-Inspired Radicalization and Terrorism in the West, he outlines 12 indicators of radicalization, including:
- Expressing vocal opposition to Western values.
- Spending lengthy amounts of time on violent jihadist websites.
- Exhibiting hatred towards non-Muslims, moderate Muslims or Shia Muslims.
- Isolating themselves from people who disagree with them.
He cautions that while all homegrown radicals exhibit some or all of these behaviours, not everyone who shows these warning signs crosses the line into violence and criminality.
People with friends or family members who fit this profile shouldn't necessarily make accusations or call 911, he said. Instead, just talk to them and find out what's going on.
"These are warning signs. In the same way that if you think someone is engaged in gang activity or illegal substances or whatever, you don't just kind of sit back and say 'Oh that's interesting.' You take action."
A previous version of this story placed the estimated number of ISIS foreign fighters at 200,000. In fact, according to CIA estimates, that number is closer to 20,000-30,000.Nov 21, 2015 1:41 PM ET