Nakhon Si Thammarat's Thung Song Prison director Phichit Wannajit and two officers were injured in a shooting while they were drinking in front of a guard's home in Tambon Tham Yai on Tuesday night.
The shooting, involving three or four assailants who pulled up in a sedan, took place at 10.15pm.
Police collected seven bullet casings from the scene.
Phichit, 56, was shot in the back while guard Weerasak Reungkerd, 55, was shot in a leg. Guard and homeowner Pakdi Surapakdi, 53, sustained two gunshots in the back and one on each arm.
Ten police guarded the victims, now stable, at Thung Song Hospital.
Phichit told police he believed the motive for the shooting stemmed from his strict approach to tackling the prison’s drug ring. He also said he remembered the face of one of the gunmen who walked up close to shoot at them.
However, police aren’t sure Phichit was the actual target because Pakdi was struck by the largest number of bullets.