A counterterrorism catch-and-release campaign by Canada's national police force may have prevented 10 aspiring jihadis from heading off to war, but the roundup at Montréal-Trudeau airport is raising worries about what comes next for radicalized youth.

On Wednesday, while federal and provincial political leaders applauded the police work, anti-radicalization experts said only an integrated effort involving civilians and police can deal with youth fixated on taking up arms in the Middle East or joining terrorist groups.

In Montreal, which has become a jihadi recruiting hotbed, the only tool appears to be handcuffs. In the past six months alone, at least seven youths have left the city to join the Islamic State in Syria or Iraq. At least 15 other teenagers and young adults have been arrested pre-emptively. Some have volunteered to be monitored, while others, such as those arrested at the Montreal airport on the weekend, were simply released after having their passports confiscated.

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Acting on a tip from one or more parents, the RCMP arrested the 10 youth at the airport but have released few other details. An 11th teenager was captured on video being led away from a Montreal home by investigators. None of the teenagers have been identified publicly and no charges were laid.

The government may opt not to pursue a criminal case for fear that any public trial could force it to reveal sensitive intelligence methods – a situation that is a chronic issue in Canadian counterterrorism cases.

The passport confiscations recalled last fall's terror attacks in which two lone-wolf assailants each killed Canadian soldiers after they were thwarted in attempts to travel abroad and possibly join jihadi groups. Officials provided no answer when asked how they might prevent similar backlash in the latest cases.

The arrests again turned scrutiny toward a pre-university in Montreal's east end. Four of the people arrested on the weekend attended Maisonneuve College. A total of 11 alleged extremist recruits have now come from the school, which again denied it has a radicalization problem. "It's increasingly clear youth recruitment is happening through social media," a statement issued by the school said.

Observers are increasingly asking whether the threat to Canada can be contained if the ranks of extremists and thwarted jihadis continue to grow.

The RCMP's terrorism prevention program is designed to intervene before suspects mobilize toward violence, but the details of the program remain murky. In Quebec, Premier Philippe Couillard has promised oft-delayed legislation to deal with radicalization. He said a new law will be presented within weeks, meaning it will be months before any new program is enacted.

The City of Montreal has announced a radicalization-prevention centre, but so far it amounts to a phone number at police headquarters. Mayor Denis Coderre said Wednesday that much work remains to be done.

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"How many parents will have to call the police or the RCMP on their children because it's all they have for tools to prevent radicalization?" said Agnès Maltais, an Opposition member of Quebec's Legislature.

Vern White, a police chief turned senator, pointed out that police cannot put released suspects under surveillance indefinitely because monitoring can require as many as 25 officers per target.

"I do have confidence if charges are warranted they will be laid… If this is an early intervention, [police] might have gotten to this before they crossed the line into criminality," Mr. White said in an interview.

But, he added, authorities have to learn how to de-program extremists – and quickly. "Now it becomes a de-radicalization discussion."

Civilians who are trying to set up anti-radicalization efforts say they're getting little support and are struggling to build trust – both among police and parents who suspect their children may be radicalized.

"You know things have already gone sour when the police are involved," said Abdul Rashid Anwar, a leader in the small Montreal Ahmadiyya community who is trying to get anti-radicalization efforts off the ground in the city but is having little success. "Parents, teachers, community leaders have to do the work of educating these kids before the police get involved. We seem to be missing the bridge from one side to the other."

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Christianne Boudreau, an Alberta woman whose son was killed in 2014 fighting with the Islamic State, is working with a public outreach program called Extreme Dialogue. She says a hardening stance in law enforcement combined with a recently enacted federal anti-terror law are making it even harder for police to reach for tools beyond arrest and detention. "Every police force is different, but some of them are hesitant. Some have their hands tied. Crown prosecutors often have their own agenda, too," she said.

Amarnath Amarasingam, a terrorism researcher who is studying Canadian foreign fighters, said it is significant that no charges have been laid in Montreal.

"I think it shows just how difficult this issue is. Tracking these individuals and understanding their networks and intentions is enormously complicated," he said. "I think, perhaps, the government is trying to move away from approaching this from strictly a law-enforcement angle."

The size of the alleged cluster caught in Quebec is large, possibly uniquely so in North America, where smaller-scale interdictions against "high-risk travellers" and "foreign fighters" have become commonplace. The Montreal case is also significant because police pounced without pursuing any immediate criminal charges or peace-bond conditions.

Charges may yet come, but investigations such as this may be the new normal. Ever since the self-proclaimed Islamic State started to seize swaths of Iraq and Syria, jihadi siren songs on social media have enticed a growing pool of would-be recruits from the West. The conflict has no end in sight and police are increasingly put into the position of trying to stop suspects who cannot be proven to have broken any laws.