Police said Bancha shot dead Sgt Wichien Priksri with his M16 assault rifle. Sgt Wachira Boonlam, Sgt Sanon Muadthip and Sgt Wikorn Chumchrt were injured and rushed to the Yala Hospital.
Police said Bancha appeared high on methamphetamines and had to be detained and allowed to calm down before he could talk to interrogators.
Bancha admitted to police that he was addicted to methamphetamine before he was conscripted and continued to use the drug.