Police in Wenzhou, Zhejiang province, are investigating a case in which a former detention center inmate claims he was sexually assaulted by a fellow inmate.

The former inmate, a 17-year-old man surnamed Xiang, told news website thecover.cn that he was assaulted several times at a detention center in the city's Lucheng district last year.

In an online statement released on Tuesday, the police said they are investigating possible violations of the law and Communist Party of China disciplinary regulations.

A spokesman for the district government, who asked not to be identified, said in an interview on Wednesday that the police investigation has been hampered by the loss of video surveillance evidence inside the detention center.

"The incident reported by the person involved took place about six months ago, while the video footage inside the detention center can only be traced back three months," he said.

The police will not shield any criminal behavior or malpractice during the investigation process," he said, adding that it will not be possible to get a quick result.

Xiang alleged that he was sexually assaulted by an inmate identified as Ye Kenong.

He also said that he tried reporting the assault to the officer who was in charge at the detention center, but his efforts were in vain.

"He told me it was a regular thing in the detention center," Xiang said. "There were even such cases in the detention rooms for women. He told me to stop making futile efforts."

Xiang also alleged that the officer had helped bring cigarettes to inmates in the detention center.

"Ye could also leave the detention room to share a cigarette with the officers if he wanted," he said, adding that there were several other inmates who had similar privileges.

He also said Ye sometimes received cooked meals delivered from outside the prison.

The incident followed several other scandals involving the country's prison system.

In December, four former prison guards in Heilongjiang province were handed jail terms from a year and four months to 2 1/2 years for turning a blind eye to a male prisoner who seduced and blackmailed a number of women using WeChat while behind bars.

The prisoner, Wang Dong, who has been in Nehe Prison since December 2012, used the messaging app to contact several women who lived near the prison and "established lover relationships with them" during his incarceration. They were brought into the prison to visit him.

In another case, in September 2014, three prisoners escaped from Yanshou county jail in Heilongjiang. The prisoners, including a death row inmate, had developed a friendly relationship with a guard and were allowed to visit him in his room. They ultimately killed him and used his uniforms as disguises when they escaped. All were captured, and two were later sentenced to death. The other was given life imprisonment.

Contact the writers at xuwei@chinadaily.com.cn