Police are hunting gunmen who killed four men at a school in Nakhon Si Thammarat yesterday.
Officers believe the victims were specifically targeted and the murders might be the result of an ongoing dispute.
One of the dead victims, Kriengkrai Chumthong, 47, was facing murder charges over his alleged involvement in the death of the wife of the mayor of Tambon Khaochum Thong in Ron Phibun district in 2013.
The bullet-riddled bodies of Kriengkrai and another three men were found near a pickup truck parked in front of an abandoned building in Ban Don Tanot school in tambon Suea Hueng in Chian Yai district, according to Chian Yai duty officer Pol Capt Sukamol Suleedamrongwut.
Evidence that another pickup truck might have been at the scene was also found.
The other three victims were Somchai Homkhao, 40, Thawat Buathongkham, 37, and Pricha Iadkaeo, 35. The bodies were sent to Chian Yai hospital.
Officers at the crime scene said two of the victims had been handcuffed next to the pickup truck.
Police also found many spent bullets from various guns including an M16 assault rifle.
Forensic officers collected items from the crime scene, including a liquor bottle which they believe belonged to the killers.
Locals near the school told officers they heard the sound of gunshots from the area around 2am yesterday.
Police suspect the killers arranged to meet the four men at the school, which is in a remote location.
The motive for the crime is still unclear, but officers think it could be related to a land dispute or an act of revenge.
Investigators will start their probe by looking at whether the men had criminal records.
Police have been monitoring Kriengkrai since the charge against him concerning the murder of the mayor's wife was forwarded to court, according to deputy superintendent Pol Lt Col Chokdi Simueang.
In 2010, gunmen fired bullets into the house of Tambon Kao Chumthong's mayor Pairote Umnakmanee, killing his wife and injuring another four relatives.
The shooting happened shortly after the mayor had left his house. Kriengkrai was arrested along with a number of other suspects after the shooting.
According to investigators, Kriengkrai, a resident of Nakhon Si Thammarat's Cha-uat district, was linked to many powerful people in his home district and Phatthalung's Muang district. He was also a younger brother of a kamnan in Cha-uat district.
Investigators also found the other three victims were involved with a criminal organisation in Phatthalung.
The four men were probably armed but the killers took their weapons after the shooting, Pol Lt Col Chokdi said.