Officials earlier gave a total toll of eight dead and said students were among the victims.
Two teachers and three other school staff were killed at the secondary school in Nonthaburi province, bordering Bangkok, a statement said.
Emergency workers directing students to safety as security personnel secured the area following a school shooting in Thailand, Aug. 7, 2026. Video by Viory
The suspect, a 14-year-old boy, was also accused of earlier killing two of his grandparents at a home in the province.
The perpetrator also died, the statement said, with a police official telling AFP he had killed himself.
