NONTHABURI: Relatives of the 14-year-old suspect in Friday's deadly shooting at Debsirin Nonthaburi School described him as a quiet, well-behaved teenager who spent much of his time playing computer games, while investigators examining his computer found evidence that he had viewed videos of school shootings in the United States in the days leading up to the attack.

The latest findings emerged as police continued trying to establish a motive for one of Thailand's deadliest recent school shootings.

Pol Lt Gen Wattana Yeejeen, commissioner of Provincial Police Region 1, said investigators were analysing the Mathayom 3 student's desktop computer and other digital evidence. Preliminary findings indicated that he played computer games featuring violence, while officers were also examining other online activities that may help explain the attack.

Reports said a review of the computer found five video clips related to school shootings abroad that had been viewed since July 30, about a week before the incident.

However, authorities stressed that they were still examining the files and other digital evidence and had not established whether the videos were directly linked to the suspect's decision to carry out the attack.

Grandparents found dead

Police and forensic officers on Friday searched the suspect's home in Bang Bua Thong district, where they found the bodies of his grandparents, Somjit Yimruang, 73, and his 74-year-old wife.

Investigators believe the teenager shot both grandparents before travelling to the school.

Somjit was found dead in a ground-floor kitchen, while the body of his wife was found in an upstairs bedroom. Initial examinations indicated that Somjit was shot in the back, with the bullet exiting through the front of his body. The grandmother is believed to have been shot while asleep.

Police suspect the teenager locked the front gate from the outside before leaving for school to prevent the bodies from being discovered.

Neighbours did not initially report hearing gunshots, Pol Lt Gen Wattana said, because the house was in a quiet area with few nearby residents.

The 9mm handgun used in the attack was legally registered to the grandfather.

'No one expected this'

The suspect's uncle, the youngest son of the slain grandparents, said the boy had lived with them since childhood after his parents separated.

He described the teenager as a reasonably good student who was extremely quiet, spent most of his time on computers and rarely went out. There had been no obvious signs of stress, conflict or behavioural problems, he said.

The uncle added that his father had never allowed family members to play with firearms and normally kept them locked inside his wardrobe. He could not explain how his nephew had discovered where the key was hidden.

Another relative, Thanunporn Yimruang, 60, the grandfather's sister, said the boy had been raised with great care by his grandparents.

She said the grandfather, a former bank manager, would see him off to school each morning and pick him up afterwards. The couple always treated him kindly, she noted.

According to Ms Thanunporn, the boy had no close group of friends, rarely left the house and spent most of his free time playing computer games.

She described him as polite and well-behaved, saying no one could have imagined such a tragedy.

Investigation continues

Forensic officers have cordoned off the house while reconstructing the events surrounding the grandparents' deaths and collecting scientific evidence.

National police chief Pol Gen Kitrat Phanphet has ordered investigators to determine whether the teenager had received any firearms training or developed shooting skills elsewhere, noting that preliminary inspections showed the fatal shots struck vital areas of the victims' bodies.

On Friday morning, eight people were killed and at least 22 others injured after gunfire erupted at Debsirin Nonthaburi School in Bang Kruai district. The dead included five teachers, the suspected gunman and his grandparents.

Prime Minister Anutin Charnvirakul expressed condolences to the victims' families and ordered urgent assistance for the injured. He said the tragedy reinforced the government's decision not to renew permits for carrying and possessing firearms.

Ninth victim