Police officers and forensic police work at a residence where the suspect lived with his grandparents who were slain before the shooting at Debsirin Nonthaburi School on Friday.

Tananchai Keawsowattana/Reuters

The gunmen suspected of carrying out a deadly attack at a school north of Bangkok searched for and viewed websites related to mass shootings before the incident, police said.

Police have seized nine computers or electronic devices from the suspect’s residence as part of their investigation into Friday’s attack, which left at least three students and three teachers dead.