They have become the Mounties of a modern China, a group of tireless polyglots willing to brave deprivation and even Ebola to nab their quarry from the most distant corners of the Earth.

Few tactics are off-limits to the investigators of China's global anti-corruption operation, dubbed "Fox Hunt," as they track down businessmen and functionaries China accuses of fattening their wallets with dirty money. They sneak across borders under false pretenses, lean on family members and blanket the world with cellphone messages to cajole and threaten suspects, all in the name of doing the Communist Party's cleanup work.

But as China takes its Fox Hunt deep into foreign nations it accuses of harbouring the guilty, it has created problems for countries caught between a desire to expel people hiding illegal funds and concerns about the Chinese judicial system.

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Of the fugitives China placed last year on a list of top-100 most wanted, 26 were believed to be in Canada, putting Ottawa squarely in Beijing's crosshairs.

Now, Canada's agreement to begin discussions with China on an extradition treaty has added fresh urgency to questions of whether Western nations should co-operate with an authoritarian government whose police, in the view of Canada's own Minister of Public Safety, torture and commit extrajudicial killings.

Prime Minister Justin Trudeau defended rapprochement with China this week, saying "Canada has extremely high standards on extradition treaties" and a "very, very rigorous process that conforms with the expectations and the values of Canadians."

But lawyers, human-rights advocates and an alleged fugitive caution that greater co-operation with China's Fox Hunt threatens to further ensnare Canada in the controversial workings of an audacious Chinese global dragnet.

Through interviews, cellphone-chat transcripts, state-media accounts and Canadian court documents, The Globe and Mail has assembled a detailed look at China's continent-spanning search for those it calls fugitives – and the longstanding problems its tactics have posed for Canada and the suspects compelled to return.

'They started targeting my family members'

Corruption in China has flourished over decades of breakneck growth and heavy government spending. Between 2003 and 2012, some $1.6-trillion in illicit funds poured out of China, a study by research group Global Financial Integrity found, more than any other country. Over a similar period, the People's Bank of China estimated 16,000 to 18,000 corrupt Chinese were on the run. The operation to pursue them has become a critical component of a domestic anti-corruption campaign under President Xi Jinping: Choke off avenues for escape, and the crackdown at home becomes more effective.

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In August, China said "Fox Hunt 2016" had already nabbed 409 people "hiding" overseas. (One of the top-100 most wanted returned to China from Canada on Thursday, local Chinese media reported.) A different but similar "Operation Skynet" has further expanded the number of banks and government departments that have joined the hunt, which mixes a campaign against graft with an effort to quash political rivals.

"They want to send a message that even though you run away, we are still after you," says Lance Gore, a professor at National University of Singapore who has written on the Fox Hunt. "There are cases where they persecute family members, or threaten them. In a Western context, of course, that's illegal. But in China, that's considered by the authorities as normal."

In an interview, one alleged fugitive in Canada described being contacted by an unknown man whose questions strongly suggested he was a Chinese security agent. "After they approached me, my family members in China all ran into trouble," said the person, whom China accuses of corruption. "They started targeting my family members."

The experience has left the alleged fugitive frightened to speak out, for fear of consequences back in China. The Globe is withholding identifying details. "Initially I felt that Canada is a fair and safe place. Now that they are going ahead with an international extradition treaty, I am a bit worried," the person said.

The problems with Chinese tactics, after all, have long been known to Canadian authorities. Chinese agents have slipped into Canada under false pretenses as far back as 2000; more recently, officers have entered as tourists, The Globe and Mail reported this week. The RCMP and the Canadian Security Intelligence Service have both launched investigations.

On a visit to Canada this week, Chinese Premier Li Keqiang denied knowing about surreptitious travels by Chinese police. "We strictly follow international law and international norms, and we also respect the law of other countries," he said.

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Australia and the United States have both publicly called on Beijing to stop the practice, which China's own government-controlled media have acknowledged. Late last year, a report in the Communist Youth League-published Beijing Youth Daily detailed "general working procedures" for China's hunt for fugitives: "The procuratorate will contact the fugitive, or send working staff to the country where the fugitive is." It looks to influence the person's "thoughts," using negotiations "and other ways in hope that he could return to China," the report said.

Cellphone messages obtained by The Globe show the mix of incentives and threats China employs. In WeChat conversations with the family of an alleged fugitive living in the U.S., a local party discipline committee and the public procurator's office offer leniency if the woman returns to China and urge her not to consult with a U.S. lawyer.

One message says the "life and career" of the suspect's family will be affected if she does not return. "I don't think you would want to have your [family] being pulled down for your silly behaviour," reads another.

The Chinese government dispatched relatives to the U.S. to pressure the woman. Consular officials delivered a similar message. But the woman is "very tough, very firm" and remains opposed to returning, said New York immigration lawyer Li Jinjin. "She does not believe anything from Chinese officials. She knows they cannot be trusted. She knows they lie every day."

Beijing's push for extradition treaties

China's globe-trotting graft-busters have taken on a kind of hometown celebrity, their work held up for praise by state media, which laud their cunning and dedication.

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A delegation landed in Nigeria in the midst of the Ebola outbreak, only to have one person come down with a high fever. They continued their work when the person was diagnosed with malaria.

"Behind the tough journeys are captures like those performed in Hollywood movies," state media crowed last year.

But there is only so much China can do without foreign co-operation, so it has also hunted extradition treaties, including with Western democracies. This week marked the first time since Paris ratified an extradition pact last year that France sent a person suspected of embezzlement back to China.

Australia, too, has signed an extradition treaty, and has signalled it will soon ratify it. China's "justice system is still very imperfect," said Philip Ruddock, a former Australian attorney-general who is now the country's special envoy for human rights. But, he asked, can foreign nations push for improvement "by simply berating them?"

"I would have negotiations. I think it's important," he said. "Over time, China is going to change even more rapidly than we've seen today. And it's engagement that's going to help."

A well-drafted extradition treaty "potentially raises the standards of the Chinese criminal justice system," argues John Gibb-Carsley in a graduate thesis on a possible Canadian deal with China. Mr. Gibb-Carsley is a lawyer with Justice Canada, although he says his views are his own.

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It would also "show the world that Canada is no shelter for the corrupt," said Zhuang Deshui, deputy director of the Peking University Clean Government Center. "This will be helpful for Canada's national image."

A formal treaty, too, could bring more stringent scrutiny to extradition requests than is typically now the case when people are deported.

And even if an extradition deal takes years to negotiate, Canada is taking other more immediate steps. In Ottawa this week, the two sides signed an agreement on the sharing and return of forfeited assets. It is a first for China, and provides a "powerful weapon for China to more effectively recover the transferred state-owned assets and reinforce the global effort to fight corruption," Xu Hong, a director-general in China's foreign ministry, wrote in a column published by the Communist Party-controlled Global Times.

Other nations have been more skeptical. The U.S., Britain and New Zealand have refused to formalize extradition deals.

Blind to China's lack of due process?

Years of Chinese deportation demands in Canada have brought to the surface numerous problems.

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Last year, the Canada Border Services Agency tried to bar a retired Chinese police officer from Canada because he had worked for China's Public Security Bureau. In arguments before the Immigration and Refugee Board of Canada, the Minister of Public Safety and Emergency Preparedness, who oversees the border services agency, argued that the Chinese police organization had "engaged in human-rights abuses over an extended period of time."

That argument is contained in an August, 2015, decision which also found "ample evidence" of torture, unlawful arrests and extrajudicial killings by the PSB, saying Chinese police "were involved in crimes against humanity."

But in many other cases, lawyers for the Canadian government rely on the same Public Security Bureau for evidence. In one case, prosecutors in Vancouver called the deputy head of the economic-crime investigation department at the Shanghai Public Security Bureau to testify against a former steel trader accused by China of fraud.

"Simply because a witness is from an authoritarian state does not mean that their evidence is automatically unreliable," an Immigration and Refugee Board member wrote in that case.

Chinese courts, too, rely heavily on hearsay evidence and bow to orders from police and Communist Party leadership, while defendants in criminal cases rarely have proper legal representation.

When they accept evidence from China, organizations like the Canadian Border Services Agency are "closing their eyes to the reality of the lack of due process in China," said Canadian lawyer Lorne Waldman, who has represented numerous Chinese fugitive suspects in Canada.

"They're willfully blind," he said.

In some cases, Canadian diplomats have been scolded by judges in Canada for giving personal details on refugee claimants to Chinese police. The CBSA declined to respond to questions about evidence from China. "Evidence in removal cases can take many forms," wrote spokesperson Esme Bailey, giving as examples records from banks, courts, corporate documents and religious institutions.

In China, legal experts have lashed back at foreign criticism, saying it has been stoked by misinformed media and lawyers trying to keep clients from extradition.

"We are currently pushing forward reforms across the entire legal system to improve court independence in trials," said Prof. Zhuang. "This shouldn't be a major reason to refuse extradition requests. It should be up to whether a suspect's behaviour is corrupt."

A Canadian treaty with China would almost certainly demand that suspects not be executed. It could also require China to videotape interrogations and court proceedings as proof that a suspect has not been mistreated, and require pretrial access to suspects for Canadian diplomats.

Beijing has already shown willingness to agree to such demands, as it did when Canada returned accused smuggler Lai Changxing, once called China's most-wanted fugitive. Still, the issues are complicated. In the Lai case, Canada monitored his treatment before trial, but not since his life sentence. "The Lai conditions in my view were not respected because Lai is not receiving adequate medical care in prison," said Winnipeg-based David Matas, who was Mr. Lai's lawyer.

It's not the only time China's promises have been called into question.

In a case that unfolded over nearly a decade, businessman Li Dongzhe and his brother fled to Vancouver to evade corruption charges, only to spend years negotiating a return home with the Chinese consulate.

After securing a verbal promise that he would do no time in jail, his brother flew back to China. Mr. Li returned, too, when Chinese diplomats promised him leniency and said his family could reclaim any legitimate assets that had been seized. Instead, a Chinese court confiscated all of Mr. Li's assets and sentenced him to life in prison. His brother received a 25-year sentence.

The brothers "tried the co-operative method. And it backfired on them horribly," said Douglas Cannon, Mr. Li's Canadian lawyer. "The deal was absolutely worthless to the Chinese authorities."

If Canada negotiates an extradition treaty, then, how can it rely on Chinese assurances? he asked. "They simply cannot be trusted. And they demonstrate this over and over again," he said.

With reports from Yu Mei and Joanna Slater

With reports from Yu Mei and Joanna Slater