File photo of Wang Dong.

An investigation into a prisoner who reportedly defrauded two women and allegedly had sex with another at the prison has confirmed that the suspect forced them to come to prison by using their naked videos as threats, dbw.cn reported.

The official probe concluded that the inmate, surnamed Wang, swindled more than 110,000 yuan ($17,717) from two of the victims after he befriended them through a phone chat platform.

The prisoner met the women in the meeting hall and dining hall at Nehe Prison, Northeast China's Heilongjiang province, but only during work days and always under strict monitoring by CCTV cameras and guards, according to the probe.

This is the third time that Wang Dong was jailed. He was first sent behind bars in 2005 for robbery, for fraud in 2009 and for kidnapping in 2012, Oriental Morning Post reported. He was 58 days short of his 18-birthday when he was first imprisoned in 2005, according to the newspaper.

He was living a comfortable and carefree life in the prison since being sent there in Dec 2012. He had easy access to banned items in prison because he was rich, Oriental Morning Post said.

His money originated from women outside the prison he befriended via WeChat, a popular mobile messaging/service platform in China. He had at least seven mistresses, the newspaper said.

A source close to Wang Dong told the newspaper that several prisoners gathered around him and gave their advice when Wang chatted with mistresses via WeChat. It went to the extreme that even a prison guard helped him write a message to his mistress.

The prison authorities confirmed Thursday that some prison guards violated relevant regulations and neglected their duties, dbw.cn reported.