The court found Pol Maj Kiartisak Somsuk, former inspector of Krathumban police station in Samut Sakhon, 14 other officers, and seven civilians guilty in collaborating to help an influential figure and his gunman conceal evidence related to the high-profile murder case.
Praween Chanklay, alias Kamnan Nok, an allegedly influential figure in Nakhon Pathom, was among seven civilians found guilty of assisting the 15 police officers to commit malfeasance and dereliction of duty.
Only one police officer, identified as Pol Sgt Maj Apirak, was acquitted.
The 15 police officers were invited to a party thrown at Praween’s house on September 6 last year when Pol Maj Siwakorn Saibua, an inspector at a highway police station, was gunned down at the dining table by Thananchai Munmak, an aide of Praween.
Thananchai was later killed while allegedly resisting arrest after he had fled Praween’s house as the 15 police officers looked on.
The 15 officers were found guilty by the court for either failing to act to stop the gunman or to send Siwakorn to a hospital in time to save his life.
The shooting happened after Praween allegedly tried to force Siwakorn to allow his fleet of trucks with legally overweight loads to pass through road checkpoints under his jurisdiction, but Siwakorn, known for his integrity, refused to comply with the request.
Once he refused, Thananchai gunned him down in front of the party-goers, including the 15 policemen.
The case led to exposure of the system used for clearance of trucks with loads over legal limits.
The 15 policemen were given different jail terms.
Kiartisak, the highest-ranked officer to be found guilty in this case, and three other officers were jailed for two years.
Eleven police officers and five civilians were given one year and four months in jail.
Another civilian was sentenced to one year, nine months and 21 days in jail.
Praween himself was given two years in jail. He was also facing another criminal charge for allegedly masterminding Siwakorn’s killing.
Three other police officers and three other civilians were given two-year suspended jail terms.
The case against the gunman has been dismissed because of his death.