Chaiwat and three park officials were suspects in the disappearance and death of Porlajee “Billy” Rakchongcharoen, who had been campaigning for the rights of ethnic Karen villagers to live in the park.
He was last seen on April 17, 2014, when he was detained by Chaiwat and other park officials at the park’s Ma Rew checkpoint in Phetchaburi province.
The Department of Special Investigation confirmed in September 2019 that they found the remains of Porlajee in a 200-litre oil drum submerged near a bridge by Kaeng Krachan Dam in Phetchaburi province.
The four suspects were charged with premeditated murder, criminal intimidation with weapons, unlawful detention, and concealing a corpse.
The Central Criminal Court for Corruption and Misconduct Cases found Chaiwat guilty of dereliction of duty for failing to write an official report on Porlajee's detention.
Chaiwat will serve a three-year jail term with no suspension.
The court, however, acquitted the four suspects of premeditated murder and concealing a corpse due to inadequate evidence.