Michael McMahon, 57, a retired New York Police Department (NYPD) sergeant turned private detective, was convicted in federal court in June 2023 alongside two co-defendants.

The three men were accused of working in a global operation dubbed "Fox Hunt," which US authorities said aimed to secretly force Chinese expats' return.

Beijing has defended the operation as part of an anti-corruption campaign and said its law enforcement agencies follow international laws when abroad.

But Washington has accused the operation of targeting dissidents and opponents of Chinese leader Xi Jinping.

"Between approximately 2016 and 2019, the defendants and their co-conspirators participated in an international campaign to threaten, harass, surveil, and intimidate" both the unnamed victim and his family, the US Department of Justice said in a statement.

Their aim was "to force him and his wife... to return to the PRC to face purported corruption charges," it added, referring to the People's Republic of China.

McMahon's Chinese co-defendants, Zhu Yong and Zheng Congying, were sentenced to 24 and 16 months in prison in January.

The ex-cop was also ordered to pay an $11,000 fine.