Army adviser and suspected human trafficker Manas Kongpan, 58, stood firm in maintaining his innocence during a marathon questioning session overnight, but was later charged on 13 counts on Thursday.
After his surrender at the police headquarters in Bangkok on Wednesday, Lt Gen Manas was immediately taken to Hat Yai police station in the southern province of Songkhla for interrogation. A forward command post of the regional police branch is housed there.
His questioning lasted from 4pm to midnight. Two teams, police interrogators and public prosecutors, took turns questioning him over the eight hours.
Lt Gen Manas insisted he had nothing to do with the trafficking of Bangladeshi and Rohingya migrants from Bangladesh and Myanmar through southern Thailand to Malaysia.
Army legal officers and soldiers from the 42nd military circle in Hat Yai observed the questioning.
The three-star general was then formally charged on 13 counts, the same as the other 51 suspects in the southern human trafficking case who are in police custody.
The charges include trafficking in persons including children, smuggling of aliens into the country, detaining them, holding them for ransom, committing transnational crime, assaulting victims, and concealing their bodies.
Police interrogators denied his request for temporary release. He was kept in an interrogation room at the Hat Yai police station because police have a deal with the military and not put a military suspect in uniform in a cell.
On Thursday police were to seek permission from the local Na Thawi court to extend the general's period of detention.
Police have 84 suspects in the human trafficking case so far, with 52 of them now in custody and 32 others still at large.
Authorities are prosecuting them after finding many live and dead Muslim migrants, graves and detention camps in a border mountain range in Songkhla province over a month ago. Malaysian authorities have also found graves on their side close to the border and they are being examined.