Two Filipino teens, who reportedly killed three fellow students and injured several others in a rare Philippine school shooting, planned the attack in advance, police said Tuesday, revealing one had trained at a firing range.

Determining a motive, however, remained a work in progress, with bullying cited as a factor but the police suggested "online influences" had also played a role.

"All indications point to the fact that it was planned," PNP (PhilippineNational Police) spokesperson Col. Allen Rae Co told a Tuesday afternoon press briefing, adding the two boys had huddled in the restroom for more than an hour the morning of the shooting.

The tragic incident occurred at San Jose National High School in Tacloban City on Monday, June 22. The two junior high school students, armed with handguns, opened fire, resulting in the tragic deaths of three fellow students and wounding 15 others. Police Regional Office 8 swiftly took the two suspects into custody.

Investigations have revealed that the attack was premeditated. Co noted the suspects' deliberate preparation included one of them receiving training at a firing range.

While investigators are looking into bullying as a potential trigger, they are also examining the impact of "online influences" on the suspects. "All indications point to the fact that it was planned," Co reiterated during the briefing.

Policemen stand near the crime scene of a shooting incident at San Jose National High School in Tacloban City, Leyte on Monday

Explainer: Tacloban school shooting raises alarm on Philippine schools safety, student welfare Philippines' Marcos orders probe into school shooting that killed 3 teens, injured 7 Philippines school shooting renews global push for safer schools