BEIJING -- A Chinese whistleblower holding secretly filmed sex tapes featuring city bureaucrats has come under pressure from police to hand them over for an investigation into an embarrassing scandal that has already cashiered 11 officials.

Police questioned Zhu Ruifeng, a former journalist who triggered the scandal in the southwestern city of Chongqing, for seven hours Monday about the tapes and said he could be liable for prosecution if he did not surrender them.

"The police were very polite but they said they wanted the videos. I firmly refused to give it to them because I have to protect my source. This is impossible," said Zhu, who lives in Beijing but was, he said, interviewed by Chongqing police officers. "They threatened me with the law, saying I could be accused of concealing evidence."

The first high-profile case broke in November after Zhu released online a video of a 50-something Communist Party district official having sex with a woman allegedly hired by developers in an extortion bid.

The leak led to the official's firing but the scandal broadened Friday as 10 other officials also caught on sex tapes were sacked.

Few details have been officially released but state media reports say the bureaucrats had sex with women hired by developers who secretly videotaped the trysts and later used the footage to extort construction deals from them.

The expanding scandal comes as China's newly installed leadership has vowed to crack down on rampant official corruption that threatens the party's legitimacy. Even as China's new Communist Party chief Xi Jinping has repeatedly pledged to strike hard against graft, authorities have been faced with a steady stream of bribery cases and other malfeasance.

Zhu said Monday's interview followed a visit by two police officers to his home in Beijing late on Sunday night in which they banged on the door and yelled at him to let them in.

Police are entitled to question a witness and request evidence in the process of an investigation, said one of Zhu's lawyers, Li Heping, who accompanied Zhu at the police station. But the whistleblower should also have a right to refuse on the basis of needing to protect his source, Li said.

He said such police pressure could discourage others from reporting official malfeasance. Zhu says he obtained the video from someone inside the Chongqing Public Security Bureau who gave it on condition of anonymity.

"If a person acts as a whistleblower and police come and demand that they hand over everything, it will not be helpful for fighting corruption and protecting media freedom," Li said.

An officer who answered the phone at the Beijing Dewai district police station where Zhu was questioned said he was not clear about the case. He referred further questions to the city's public security bureau, which did not immediately respond to a faxed list of questions.

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