Pol Lt Col Prawut Wongsinin made the announcement following an inspection visit on Saturday (Nov 22) to the prison in Chatuchak district with Justice Minister Rutthapon Naowarat, reports the Bangkok Post.
The Department of Special Investigation (DSI) would be put in charge of the case, said the minister, who was joined by Pol Maj Gen Yutthana Praedam, the DSI director-general, and his deputy Pol Lt Col Anurak Rojnirankit.
Pol Lt Col Prawut said he had received information about misconduct by prison staff a month after his appointment as the corrections chief on Oct 1 and reported it to his seniors.
After nearly three weeks of gathering evidence, it was confirmed that about 20 officials, both senior and junior, were complicit in violating regulations, he said.
Among other findings, investigators discovered evidence of Chinese women entering the prison, ostensibly to provide sexual services.
A raid conducted on Nov 16 found two women in their early twenties in the prison. One was alone with a Chinese inmate in a secret room and the other was waiting upstairs.
It took authorities a while to get into the room as it was secured by two locked doors. The women were found dressed up and both denied engaging in sex work when questioned, Pol Lt Col Prawut said.
However, authorities found condoms, lingerie, stained tissues, traces of fluids on a sofa, tobacco and alcohol.
Forensic officers will examine the scene on Monday, Pol Lt Col Prawut said, adding that the individuals potentially involved had been relocated away from the area.
He said Thai police had no authority to detain the two women since the facts were not clear yet. They have already returned to China, and Thai authorities would coordinate with their Chinese counterparts to blacklist them if they are found to have been involved in criminal activity.
Pol Lt Col Prawut said CCTV video examined during the investigation indicated that Chinese women had been entering the prison every Sunday. Some recordings had been deleted, he added.
The raid last Sunday also uncovered mobile phones, lighters, portable air‑conditioning units, a refrigerator and a microwave oven.
Prime Minister Anutin Charnvirakul on Friday vowed tough action against any and all officials involved in awarding special privileges to Chinese inmates.
The Department of Corrections has transferred several Chinese inmates from the prison to a more suitable facility. More than 10 others remain on their original ward, but if further misconduct is uncovered, additional transfers would be made, Pol Lt Col Prawut said.