Canadian authorities deported a violent criminal who was a former Chinese democracy activist, sending back to China a man who once sought political change at home, but committed a series of knife attacks in Canada.

For more than a decade, Yang Wei, 49, has presented Canadian courts and immigration officials with a challenging case: a man jailed in China for demanding the overthrow of the Communist regime before fleeing to Canada where he was arrested for a string of violent acts.

Mr. Yang, who became a permanent resident in 2003, left Toronto for Beijing at 2:30 p.m. on Wednesday, according to his lawyer Vanessa Leigh. Friends worry his association with an outlawed Chinese democracy party may place him at risk of incarceration when he arrives back in China. Dissident poet Liao Yiwu has taken up his cause, writing an open letter this week criticizing his deportation.

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But Mr. Yang has also been assessed as likely to reoffend in Canada where, according to Toronto police reports from 2006 to 2010, he punched a roommate, threatened a cellphone salesman with a large butcher knife, told a bus driver “I’ll kill you,” brandished a large carving knife at a men’s hostel worker and used a filleting knife to stab at a different bus driver at least 13 times. He received several suspended sentences, but also served four years in federal prison for aggravated assault and possession of a weapon for a dangerous purpose.

A court declared him a dangerous offender. He was prescribed antipsychotic medication. Permanent residents found guilty of serious crimes can be deported.

Mr. Yang “represents a present and future danger to the Canadian public” and his “presence in Canada poses an unacceptable risk,” a 2017 recommendation to the Minister of Immigration, Refugees and Citizenship found. He has little social support in Canada. “I find that Mr. Yang’s removal would not shock the conscience of Canadians,” says the recommendation, whose author is not disclosed. The department did not respond to a request for comment Wednesday morning.

The Canada Border Services Agency (CBSA) said privacy reasons prevent it from commenting on individual cases or sharing deportation information.

“Everyone ordered to be removed from Canada is entitled to due process before the law and all removal orders are subject to various levels of appeal or review. Prior to removal, individuals may seek leave for judicial review, as well as administrative review procedures that assess the potential risk to the person of returning to their country of origin,” said CBSA spokesperson Judith Gadbois-St-Cyr.

A 2018 Parole Board document noted that many of Mr. Yang’s offences were committed while on probation and said he has a tendency “not to take [his] medication which contributes to emotional instability.” A psychiatrist who examined him said he had a “substantial risk of reoffence,” even with proper medication.

Mr. Yang has also told immigration officials that he does not believe “Chinese authorities would care” if he was returned – although immigration documents note that he may not have been in a “right state of mind” when he made that statement. Mr. Yang’s sister told a social worker that his problems stem from difficulties in his “living environment” in Canada, where he had been bullied, beaten and robbed, she said.

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Mr. Yang’s removal comes in the midst of high tension between Ottawa and Beijing, following the arrest in Vancouver of Huawei executive Meng Wanzhou, and a series of measures taken by China, including the arrest of Canadians Michael Kovrig and Michael Spavor, as well as measures to block imports of Canadian canola and meat.

Mr. Yang faces potentially serious consequences in China, which he fled as a wanted man, said Sheng Xue, an activist in Canada who hosted him at her home after he arrived.

It “is so dangerous for him to go back to China,” Ms. Sheng said. “Canada cannot do this.”

Mr. Yang was a teenager in China when he heard about the bloody government response at Tiananmen Square, where troops killed hundreds – perhaps thousands – of demonstrators in 1989. In response, he posted flyers “calling for an uprising to overthrow the dictatorship,” Ms. Sheng said. “He was very brave.”

According to Canadian court documents, Mr. Yang said he was jailed three years for treason.

After his release, Mr. Yang joined a democracy party and was fleeing arrest in 1999 when he escaped the country.

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According to Mr. Liao, Mr. Yang at the time chanced upon a village funeral procession and bought the deceased man’s identification card. He used an altered version to join a tour group to Thailand, but struggled to obtain refugee status there.

“He lived for a while like a wild dog on the streets of a foreign country. One day after he’d passed out from hunger, he was rescued by Thai monks and brought to a Buddhist temple,” Mr. Liao wrote in a letter.

Mr. Yang eventually received refugee status and was welcomed to Canada. But Ms. Sheng noticed signs of mental difficulty from the moment he arrived. She believes “his health was damaged when he was in prison in China.”

“I feel very sorry for him,” she said.

Mr. Liao, too, said he worries about Mr. Yang, and his future in China.

“I do know that his old case in Sichuan [prison] is not finalized,” he wrote. “According to the current state of retrogression in China, once he’s repatriated, his life will vanish in the prisons of the dictatorship.”