First he shot dead his two grandparents, using his grandfather’s handgun, then went to a secondary school in Nonthaburi province, bordering Bangkok, and killed five school staff, national police said in a statement.
The 14-year-old perpetrator also died, the statement said, with a police official telling AFP he had killed himself.
Officials earlier gave a higher toll and initially said students were among the victims.
Dozens of police and emergency responders gathered outside the cordoned-off Debsirin Nonthaburi School, AFP journalists saw, while parents waited to pick up their children and tearful students and staff comforted each other outside.
“I was afraid that I would die, and I was scared that I wouldn’t be able to pursue my dreams,” said Pawarisa Maylissa, a grade 12 student who hopes to attend medical school.
“I heard many gunshots very loudly because it seemed the suspect was on the floor directly above us,” she told AFP.
Prime Minister Anutin Charnvirakul told reporters at the scene that “police interrogated his close friend who said the suspect had been under stress” related to his schooling.
“His actions also suggested that he had clearly planned” the assault, Anutin added.
“The gun was a registered firearm and was kept at a house, but somehow he gained access to it.”
The prime minister said more than 30 people were injured, with around nine in critical condition.
The shooter was identified by local media as a student of the school.
Purin Khumchoo, 17, said he was among the students who had nearly been shot.
“He was my junior, but I had a feeling that he was a troubled kid. My group of friends who knew him said he was interested in the FBI and guns, and that he was bullied by many other students,” Purin told AFP outside his school.
“When I saw him aiming the gun at me, I thought he looked very professional, as if he had been trained for a long time.”
Photos published by local media show the suspect wearing a purple school uniform and carrying a black cross-body bag, with several bullet casings visible on the ground.
Education Minister Prasert Jantararuangtong pledged to provide mental health assistance to students and ramp up security measures at educational institutions.
“We haven’t checked whether students have brought weapons to school. Our level of security is not that tight,” he told reporters at the school.
Thongchai Thanakat, a motorcycle-taxi driver who has worked in the area for 20 years, said he was waiting to pick up passengers outside the school when he heard more than 10 gunshots and saw a stream of students rushing out.
“Some of them weren’t even wearing shoes,” he told AFP.
Anutin earlier called the shooting “a terrible incident”, posing the question: “How could this happen in our country?”
Thailand has one of the highest rates of gun ownership in the region, with around 10 million firearms estimated to be in circulation – one for every seven inhabitants.
Past promises of tightening gun laws have not prevented repeated shootings.
Thai police shot and arrested a teenager who opened fire at a school in the south of the country in February, killing the principal and wounding two students.
The teen had stabbed a police officer with a knife, stole his pistol and then used the weapon in the shooting.
A local police chief said at the time that the suspect had been discharged from psychiatric hospitalisation.
In 2022, an ex-policeman armed with a gun and a knife stormed into a nursery in the country’s north, killing 24 children and 12 adults in one of Thailand’s deadliest massacres. (AFP)
