Police are stepping up their investigation into the shooting at Debsirin Nonthaburi School, questioning teachers, students and witnesses as they seek to determine what motivated a 14-year-old boy to kill seven people before taking his own life on Friday.

The suspect’s parents, who separated when he was young, were questioned on Saturday at the Plai Bang police station in Nonthaburi.

The father appeared visibly distressed and briefly told reporters: “I apologise to society for what my son has done. I still haven’t seen my son.”

The boy’s mother was said to be emotionally unfit to speak and declined to answer questions from the media.

Investigators will determine whether they need to be interviewed again, said Pol Col Chokchai Khanacharoen, deputy chief of the Nonthaburi Provincial Police Office.

Police are also reviewing reports that the student had problems at school, with friends or family, or was addicted to online games, in order to establish the circumstances and motive for the shooting, Pol Col Chokchai said.

As well, investigators are tracing the source of 98 rounds of live ammunition and have checked a shooting range in Bang Bua Thong for possible links to the student.

A press conference has been scheduled for Sunday at the Plai Bang police station to provide an update and summary of the investigation.

The shooting on Friday morning at the state-run secondary school in Bang Kruai district of Nonthaburi shocked the nation. Five teachers, including a school deputy director and a school secretary, were killed and at least 22 others injured, including students and teaching personnel. The boy then shot himself and died en route to hospital.

Police and forensic officers subsequently searched the boy’s home in Bang Bua Thong district, where they found the bodies of his grandparents, Somjit Yimruang, 73, and his 74-year-old wife. The suspect had lived with them since his parents separated.

Somjit, a retired bank manager, was found dead in a ground-floor kitchen, while the body of his wife, a retired teacher, 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 she slept. (Story continues below)

Police cordon off the shooting scene inside Debsirin Nonthaburi School in Bang Kruai district of Nonthaburi on Friday morning. (Photo: Chanat Katanyu)

Gun legally registered

The 9mm handgun used in the attack was legally registered to the boy’s grandfather. A CZ75 9mm semi-automatic pistol, it is a popular weapon in Thailand. Many are purchased by the government for its “welfare gun” programme, under which eligible officials can obtain weapons at steep discounts. However, many of these weapons end up being resold.

Earlier, there had been reports that a 12-year-old schoolgirl, who was critically injured and receiving treatment at Phra Nang Klao Hospital, had died.

However, on Saturday morning, news reporters contacted the hospital director, who confirmed that the girl had not died, said Channel 3 news anchor Sorayuth Suthassanachinda.

Meanwhile, relatives of the victims travelled to Debsirin Nonthaburi School on Saturday morning to perform a traditional ceremony to invite the spirits of the deceased to return home. Mourners laid flowers outside the school.

Security guards did not allow members of the media to enter the school.

The ceremony lasted about 10 minutes. After it ended, the relatives left without speaking to reporters.

A coffin bearing the body of one of the school shooting victims is brought from Police General Hospital. (Photo: Reuters)