The Philippine National Police on Monday launched an in-depth investigation into the deadly shooting at San Jose National High School in Tacloban City while exploring new security measures to better protect students and teachers nationwide.

PNP chief Gen. Jose Melencio Nartatez Jr. said investigators have been ordered to examine all circumstances surrounding the incident, including reports that one of the minor suspects may have been subjected to prolonged bullying.

"I expect a full investigation into this incident that will focus on the circumstances that led to this incident — from what prompted these minors to do this and how they were able to get these firearms," Nartatez said.

Police said the two suspects, aged 14 and 15, are already in custody and will be turned over to social welfare authorities.

Police Regional Office 8 director Brig. Gen. Jason Capoy said investigators are validating information that one of the suspects had allegedly been bullied since Grade 7.

"Hindi pa naman confirmed. Parang na-bully rin daw ito since Grade 7. Ongoing pa yung interview natin together with DSWD, mga teachers and school officials," Capoy said.

The shooting left three students dead and seven others injured after the suspects allegedly opened fire inside two classrooms. Most of the victims were Grade 9 students.

Authorities recovered a Glock pistol and a .38-caliber revolver allegedly used in the attack and are investigating how the minors obtained the firearms and brought them onto campus.

The incident has also prompted discussions between the PNP and the Department of Education on possible enhancements to school security protocols. Under existing rules, police officers are generally prohibited from entering school premises without authorization from school officials.

Nartatez said the PNP will coordinate closely with DepEd to develop measures that will improve campus safety while ensuring the peace of mind of students, teachers, and parents.