The Thai teenager who allegedly killed seven people, including his grandparents, on Friday before killing self was “under stress” and had “planned” the shooting, according to Thailand's Prime Minister Anutin Charnvirakul.A teenager opened fire at a school outside Bangkok on Friday, killing five people before himself. Before that, he had also killed his grandparents. (AFP)"Police interrogated his close friend who said the suspect had been under stress" related to his schooling, Anutin said while speaking to reporters, as quoted by news agency AFP.He made the remarks outside the secondary school in Nonthaburi province of Thailand, bordering Bangkok, where the shooting happened.“His actions also suggested that he had clearly planned (the shooting),” Anutin added.Also read: 8 dead, including teen gunman, after school shooting in Thailand; 23 injuredApart from the seven people murdered, nine out of those injured in the mass shooting incident are in critical condition, the Prime Minister said. At least 23 people were injured in the incident, according to police.Anutin told reporters he would discuss gun control with the country's police chief, reported Reuters."This is terrible for something like this to happen. I'm sad for those who died and sad for something like this to happen in our country," Anutin said.What happened?A teenager opened fire at a school outside Bangkok on Friday, killing five people before himself. Before that, he had also killed his grandparents.Also read: Thailand teen killed grandparents at home before deadly school shooting: PoliceAccording to the police, all the victims killed in the school were teachers and staff. The 14-year-old suspect fired at least 26 rounds of bullets and used his grandfather's gun. An additional 34 rounds were found, said police.This was the worst mass killing Thailand has seen since 2022. What prompted the teenager to carry out the attack is not yet certain.‘There were many shots: bang, bang, bang’The incident happened at Debsirin Nonthaburi School, which is on the outskirts of Bangkok. After the shooting, the students and teachers cried, hugged each other as they stormed out of classrooms while those injured and killed were moved to hospitals.An 18-year-old student described the horror and said that they initially thought that firecrackers were going off or someone was banging an object.“I didn't think it was a gun at first. There were many shots: bang, bang, bang. Then it went quiet. Then it started again,” he told Reuters.Notably, Thailand has the highest number of civilian-held guns in Southeast Asia and one of the highest rates of gun ownership per capita in Asia, according to a 2017 estimate by the Small Arms Survey.(With inputs from AFP, Reuters)