In mid-February, a former worker for a Chinese oil equipment company boarded a plane in Canada bound for China.

Chang Zheng was not returning home for a visit. He had been "persuaded to surrender," Chinese media reported.

His return was a celebrated accomplishment for China, which has scoured the world to haul back people it accuses of corruption. Mr. Chang, who left for Canada in 2011, had been added to China's list of top-100 most-wanted economic fugitives.

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Now, Beijing is pressing Ottawa to make it easier to bring back others like him.

As it seeks a new "golden era" of relations, China wants more "co-operation" with Canada in "combatting corruption, [the] hunt-down and surrender of fugitive offenders and recovery of illegal proceeds," China's ambassador to Canada, Luo Zhaohui, wrote in an article published by The Globe and Mail this weekend.

He did not specifically mention pursuing an extradition treaty.

But the desire for more global legal power has come from the highest levels in China, which has pointed to the United States, Canada and Australia as the largest havens for corrupt Chinese.

China must "speed up the signing of extradition treaties and establish law-enforcement co-operation with destination countries for those who have fled abroad," wrote Huang Shuxian, deputy head of the Central Commission for Discipline Inspection, China's anti-graft body, in a published article reported Monday by Reuters.

Canada is a key destination country. Of the top-100 most-wanted for economic crimes, authorities in China believe 26 may be in Canada.

Under existing protocols, Canada occasionally deports people at China's request, but China typically provides little evidence to back up allegations of wrongdoing outside of an accusation document, lawyers say.

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From 2009 to 2015, Canada sent home 1,400 Chinese people, although most of them were returned for illegal immigration.

Now, the prospect of closer legal ties with China has prompted warnings from legal experts who fault Canadian decision-makers for a naive understanding of the Chinese justice system. China routinely executes convicts, tortures suspects and detains people without charges for lengthy periods of time.

"The evidence is all out there, and we are regularly sending people back to be tortured and facing no possibility whatsoever of a fair trial. And we have really no way of evaluating the validity of even the charges against them," said Clive Ansley, an expert in Chinese law who is regularly called upon by the Immigration and Refugee Board of Canada for his views.

When Stephen Harper visited Beijing in 2014, the two countries agreed to "continue co-operation on combatting transnational crime and corruption." Canada typically demands pledges from China that it will not mistreat or execute suspects who are sent back.

But even in cases where Canada has obtained such assurances, it does little monitoring. After smuggler Lai Changxing was deported in 2011, "Canadian officials visited Mr. Lai during his pre-trial period and attended his trial," Foreign Affairs spokesman François Lasalle said.

They have done nothing to check on him since he was sentenced to life in prison in 2012.

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He "is not a Canadian citizen, and therefore officials cannot provide consular services," Mr. Lasalle said.

Earlier this year, the Law Council of Australia angrily denounced a proposed extradition treaty with China, saying Australia has no way to ensure those it extradites receive a fair trial, or to properly ensure China abides by agreements not to torture or execute those it convicts.

In February, the United Nations Committee Against Torture said in a statement on China it was "seriously concerned over consistent reports indicating that the practice of torture and ill treatment is still deeply entrenched in the criminal-justice system, which overly relies on confessions as the basis for convictions."

Only days after Mr. Chang returned to China, a former deputy director of National Energy Administration, Xu Yongsheng, told a Chinese court he had been tortured into a false confession to taking bribes.

He said he had been deprived of sleep and subjected to more than 100 interrogations – including some at locations without cameras – that left him bloodied. Interrogators threatened his family and him, with one woman saying she should cut off his head and give it as "an offering under the Communist Party flag," according to an account in China's Caixin media.

Such accounts should raise red flags in Canada, said Mr. Ansley.

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China has made legal reforms in recent years, giving trial judges a greater ability to render their own decisions and holding them personally responsible for wrongful convictions. But the changes have been limited by the Communist Party's desire to maintain supremacy.

Last year, China's supreme court called for rejection of the Western concept of judicial independence.

"There is a tendency in Canada for courts and tribunals to think that the innocent in China face no problem, that their innocence will set them free," said David Matas, a human-rights and immigration lawyer who has participated in roughly a dozen corruption cases against Chinese people.

Canadian courts and tribunals "often have difficulty appreciating the trouble that the innocent in China face who are accused for political reasons, especially when that political motivation is not express, but visible only by seeing the pattern of prosecutions."

Take Mr. Chang, whose case appears to be connected to an elite power struggle in China. His former boss, Tao Yuchun, had been a president of a natural-gas subsidiary at China National Petroleum Corp., the sprawling state energy giant once headed by Zhou Yongkang, a powerful figure whose influence Chinese President Xi Jinping has sought to disassemble.

Mr. Zhou was sentenced to life in prison last year. Mr. Tao was tried for taking bribes and embezzling public assets, although in court he loudly denied most of the charges against him.

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Canada should be very cautious when asked to send back people whose cases potentially mix politics with criminal courts, Mr. Matas said.

"Because of heavy politicization of Chinese corruption charges, the government of Canada, in my view, should have nothing to do with them unless there is substantial evidence to back them up. That is not the case now," he said.

The record of Chinese courts, with a 99.92-per-cent conviction rate, suggests caution is warranted even in cases without political overtones.

Vincent Yang worked as a criminal defence lawyer in Shanghai for six years. "It was very depressing. I lost all the cases. There was never an acquittal," he says.

Prof. Yang, a Canadian citizen who now holds a personal chair in international law at University of Saint Joseph in Macau, nonetheless argues Canada is better to sign an extradition treaty with China as a way to codify expectations.

"Sign a treaty with provisions to guarantee there will be no death penalty, no torture, no unfair trials – then at least there's a commitment made on paper," Prof. Yang said.

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"The more treaties China signs with Western countries, the better," he said. "It helps China to push ahead law reforms in China."