Mr Zhou, a resident of the United States, last year arrived in Hong Kong from Macau on a Malaysian passport under an assumed name. Hong Kong authorities stopped and detained him at the border for “problems”. After two days in their custody, he was taken by car to the border with the mainland and handed over to Chinese authorities.

After weeks of hearing nothing about her husband, Zhou’s girlfriend (mother of their 18-year-old daughter) was called by a former inmate in a Shenzhen prison who told her that he was in jail. Four months later, another inmate said he also recognised Zhou as someone he had seen in prison. Yet, prison and court authorities in China deny knowing anything about his whereabouts.

Hong Kong’s government, headed by pro-Beijing Donald Tsang Yam-kuen, has also not made any comments about the case.

According to Zhou’s lawyer, the arrest by Hong Kong authorities and the transfer of his client to the mainland constitute a violation of the legal framework based on the principle of “one country, two systems’ that was established when the United Kingdom returned the former Crown Colony to the People’s Republic of China.

The agreement meant that for 50 years following Hong Kong’s handover in 1997, civil rights would continue to be protected in the territory.

For a leading immigration consultant in the city, the Zhou’s case is “unlawful, inexplicable and without precedent”.

For Zhang Yuewei, the former student leader’s girlfriend, it is an obvious “conspiracy to abuse his human rights”.

Last week she travelled to Hong Kong to raise awareness about Zhou’s plight. The last time she saw him was on 26 September of last year.

Zhou runs an employment agency and is a US green card holder. He travelled to the mainland because he wanted to “visit his family. His father had a stroke and is partially paralysed, and his mother has heart disease.”

Zhou fled to the United States in 1992, three years after the bloody crackdown of pro-democracy protests in Tiananmen Square.

He tried to re-enter the mainland in 1998 (through Hong Kong) but was caught, imprisoned and held for three years on illegal entry charges. In 2002, he went back to the United States.

After trying in vain to obtain a mainland visa, he bought a fake Malaysian passport.

According to an attorney who was able to see him in prison, he is charged with an unspecified “crime allegedly committed in Hong Kong”.

Zhou’s case raises several questions concerning Hong Kong, where Chief Executive Donald Tsang Yam-kuen is facing calls for an official inquiry into the case.

Many Honk Kongers are in fact very concerned that cases like Zhou’s might be the start of a trend whereby the territory’s law is no longer there to protect them.

Indeed, mainland China and Hong Kong do not have an extradition treaty. Any crime committed in the territory, including immigration violations, should be tried locally or the alleged offender should be expelled to his or her country of origin.