The motorist arrested after three students were shot dead following a road accident in Krabi on Tuesday morning has attacked another prisoner in his police cell.
Police said Theerasak Boonruang, 42, punched another prisoner in his cell at Khao Phanom police station on Tuesday evening and banged his head on the floor, causing injuries.
Police pulled him off the other man and moved him to solitary confinement.
Investigators planned to continue questioning Mr Theerasak over Tuesday's deadly shooting and did not intend to take him to the murder scene for a crime re-enactment on Wednesday.
The suspect is charged with murder, illegal possession of a weapon, carrying it in public without a permit and firing it in public, and taking illicit drugs. He has admitted to the charges, according to police, saying he was under the influence of methamphetamine at the time.
Mr Theerasak was arrested after three 18-year-old students were found shot dead on the side of a road, their burned motorcycle overturned on the road nearby.
The three teens, one boy and two girls, were shot dead and their motorcycle set on fire after a crash involving a BMW on the Khao Phanom-Thung Yai Road in Phru Tiew about 1.29am on Tuesday.
Police said a BMW parked at Mr Theerasak's house had a shattered front windscreen.
The dead boy was identified as Nanthaphan Udomsri and the girls as Natnicha Phanseng and Phanthira Chuthong, all Mathayom Suksa 6 students at Phanom Benja School.
Management, teachers and students at Phanom Benja School attended bathing rites for the three students at three local temples in Khao Phanom district on Tuesday.
