Officers removed electronic devices and other items from the suspect's home, where a Nazi flag was seen hanging near the garage. Emergency responders also removed two bodies from the property.

Police said the teenager fired at least 26 rounds from a handgun belonging to his grandfather. Investigators believe he killed his grandparents before travelling to the school and carrying out the attack. The gunman later died from a self-inflicted gunshot wound.

Thai Prime Minister Anutin Charnvirakul visited the school following the shooting. He described the attack as "truly terrible" and said it should "never have happened".

Police are investigating the motive for the shooting and how the teenager gained access to the weapon.