Telling his parents he was flying to Turkey for two weeks, Mohamed Ali left Canada in April 2014 to join the so-called Islamic State.

“I traded the snow for the desert sand,” he wrote on social media after his arrival in Syria.

Four years later, ISIS is collapsing in Syria and Iraq and Canadian officials are bracing for the possible return of foreign fighters like Ali — if he is still alive — as well as their wives and children. Some have already come back.

Canada’s strategy for managing their return is detailed in documents obtained exclusively by Global News that point to the hurdles police face in foreign fighter investigations, and the alternative approaches they are trying because criminal charges have proved so challenging.

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Disclosed under the Access to Information Act, the documents are a stark assessment of the prospects that former ISIS fighters like Ali will ever face criminal charges upon their return to Canada, saying terrorism investigations are among the most difficult the RCMP conducts.

“Often, they require evidence of an individual’s activity in foreign conflict zones, or rely on information provided by partners that we are not authorized to disclose in court,” according to the documents. “The RCMP also faces challenges in collecting digital evidence, including access to encrypted communications.”

The Twitter profile photo of Mohamed Ali, a former university student from Mississauga, Ont. who joined ISIS in 2014. Twitter

Calling terrorism “complex and resource intensive,” the documents caution that “there may not be sufficient evidence for charges” and say the fallback is to “mitigate the threat through efforts outside the criminal justice system.”

The government estimates that about 190 Canadian extremists are currently active in terrorist groups overseas, mostly in Syria and Iraq. An additional 60 have returned, and police are bracing for another wave of returnees over the next one to three months.

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Few who left to join ISIS have been charged upon their return, an issue that has been raised repeatedly in the House of Commons, with the Conservatives accusing the Liberals of greeting returning ISIS members with “group-hug sessions.”

On Friday, the topic came up again in Question Period over a Toronto-area man’s confession to a U.S. reporter that he had participated in executions while serving with ISIS in Syria. He denied to Global News he had killed anyone.

WATCH: Question Period erupts over NYT podcast featuring Canadian ISIS recruit

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While the government has provided few details about how it is dealing with “returnees,” the RCMP documents reveal the standard operating procedures that have been put in place, and underscore what police have been saying quietly for some time: that they are struggling to charge returning Canadians over their involvement in terrorism in countries like Syria, forcing them to look at other options.

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Unlike the United Kingdom, which has revoked the citizenship of ISIS fighters so they cannot return, Canadians who go abroad to commit terrorism have a “right to return,” according to a Briefing Note prepared for Public Safety Minister Ralph Goodale.

“Therefore, even if a Canadian engaged in terrorist activity abroad, the government must facilitate their return to Canada,” said the document obtained by Global News.

Because Canada has cancelled the passports of known foreign fighters, they can’t come back without first going to a Canadian diplomatic post, which serves as an early warning system for the RCMP.

The return of terrorists is managed by a group within government called the High Risk Returnee Interdepartmental Taskforce, which works with the RCMP’s National Security Joint Operations Centre, the briefing note says.

A document obtained by Global News shows the government has formed an interdepartmental task force to manage the return of foreign fighters. RCMP

The task force is made up of Global Affairs Canada, RCMP, Canadian Security Intelligence Service, Canada Border Services Agency, Passport Canada, Public Safety Canada and Transport Canada.

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Once the RCMP becomes aware a foreign fighter is preparing to come back to Canada, the task force meets to discuss what measures are needed to control the return, the minister’s briefing note says.

“The taskforce allows us to collectively identify what measures can mitigate the threat these individuals may pose during their return to Canada,” an RCMP document says. “This could include sending officers overseas to collect evidence before they depart, or their detention by police upon arrival in Canada.” The RCMP also “may use undercover officers to engage with the HRT [High Risk Traveler] to collect evidence, or monitor them during their flight home.”

READ MORE: How police hunted down an Ontario terror suspect from anonymous online posts

When their flight lands in Canada, the returnees are subjected to secondary customs screening and possibly police detention.

“HRRs [High Risk Returnees] can pose a significant threat to the national security of Canada,” an RCMP document said.

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But it also listed the challenges involved in terrorism investigations: the “international nature of activities and targets”; “sharing information among partner agencies”; the “conundrum” of turning intelligence into evidence; and the reality that some terrorists “do not fear prosecution or death.”

Assuming criminal charges are not possible, police may try to obtain a peace bond from the courts to restrict their behaviour and limit their ability to go online.

But sometimes the best the RCMP can do is send an intervention team. The intervention teams can “engage with the returnee and the returnee’s family to open up dialogue with the individual and to help support the returnee’s disengagement from their radical ideology and past behavior,” it said.

“Moving forward, we must continue to work to identify how to best address returnees,” read the briefing note to the minister. “While they may have engaged in terrorism abroad and broken the law, not all returnees continue to post [sic] a threat — they may now be disillusioned with the cause.”

“The government of Canada must focus its investigative resources on those that continue to post [sic] a threat to Canada, and leverage efforts such as CRV [Countering Radicalization to Violence] to work with those who may no longer be interested in violence.”

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Foreign fighter researcher Professor Amarnath Amarasingam said 21 Canadians who had gone to Syria and Iraq were known to have died and 16 had come back — a number that includes those turned back in countries like Turkey before they ever made it to a war zone.

Only two to three returnees actually served in ISIS, he said. “Another six to seven joined other militant and rebel groups in Syria, and the remainder got caught on their way into Syria and didn’t even cross over,” said Amarasingam, a Senior Research Fellow at the Institute for Strategic Dialogue.