A teenager who shot and killed his grandparents at their home before opening fire at a school in Thailand had been bullied and was 'stressed' by schoolwork, police have revealed. The 14-year-old shooter struck his grandparents, using his grandfather's handgun, before opening fire at a secondary school in Nonthaburi province, bordering Bangkok, killing five school staff. Some 30 more were injured at the school before the suspect turned the gun on himself. The Debsirin School is a well-known secondary school in Thailand and has branches across the country. The original Debsirin School in Bangkok was founded by Thai King Chulalongkorn in 1885.