New York, New York - A former NYPD cop turned private investigator and two Chinese citizens were found guilty Wednesday in a landmark legal case taking aim at the Chinese government's illegal efforts to extort dissidents living overseas.

The three men played a part in China's years-long pressure campaign against dissident Xu Jin, a former Wuhan municipal government official, and his family, with McMahon using his investigative skills to track down where Xu lived in New Jersey, prosecutors said during the two-week trail in Brooklyn federal court.

Michael McMahon (55), a retired NYPD sergeant, and another man, Zhu Yong (66), were convicted of acting as a foreign agent and interstate stalking, while a third, Zheng Chongring (27), was convicted of stalking charges but cleared of being a foreign agent.

McMahon could face up to 20 years behind bars, Zhu 25 years, and Zheng 10 years

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Prosecutors described the scheme as part of a sweeping Chinese initiative, dubbed Operation Fox Hunt, aimed at finding so-called corruption suspects living overseas and forcing them to return to China to face charges. The Chinese government bypassed US officials and acted illegally on American soil to harass Xu in an operation run by a Chinese cop and prosecutor, prosecutors said.

The plot involved flying forcing Xu's elderly father to fly to the US and dropping him on Xu's sister-in-law's doorstep on April 5, 2017, with one mission: get his son to come back and face the charges against him.

"It was very shocking," Xu said on the stand. "I was very angry because the Wuhan officials and the prosecutor's office did things like this to an 80 somewhat-year-old man and he had a bad health condition and he was being forced to come to the US."

Zheng came into the picture in 2018, when prosecutors said he and another man banged on Xu's door, then left a menacing note reading, "If you are willing to go back to the mainland and spend 10 years in prison, your wife and children will be all right. That's the end of this matter!"

Xu testified that the visit brought the harassment to a new, terrifying level.

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"Before I saw this I felt that the threats from the Chinese Communist Party was only a mental threat to me," he told the jury. "However, when I saw that note, I realized that it had become a physical threat."

McMahon, who was paid more than $19,000, was asked to dig up information on Xu and his family, then monitored the sister-in-law's house during the elderly man's visit, all in the hopes of following Xu to his Warren, New Jersey, home, prosecutors said.

The former police officer's basic research turned up articles and other information that the Chinese government wanted to force him back to China and arrest him, prosecutors said, and some of his payment came as wire transfers from Chinese officials.

McMahon's lawyer, Lawrence Lustberg, argued that the government didn't show any evidence proving that he knew he was working for China, and that McMahon thought he was working for a private company.

"That family is a victim of Chinese misconduct. But ladies and gentlemen, so is Mike McMahon," he said.

The other two defendants' lawyers made similar arguments.

His wife, Martha Byrne McMahon, expressed relief when her husband was acquitted of a conspiracy count relating to acting as a foreign agent, then wept bitterly as the jury foreman read the remaining counts as guilty. On Wednesday, she tweeted at Arizona Rep. Andy Biggs, who is on the House Judiciary Committee, asking him to review the case.

McMahon said he was "devastated" by the verdict, and he plans to appeal.

"I did everything by the book as a licensed private investigator," he said. "Nothing in this case was out of the ordinary in what I've done in hundreds of cases... If I knew they were a foreign government, I would never have worked on this case."

All three men remain free on bond until their sentencing date, which has not yet been scheduled.