PENDLETON (AP) — Police arrested two boys accused of threatening to bomb Pendleton High School.

The threat and the discovery of an unclaimed backpack emptied classrooms Monday morning. An explosives unit found nothing in the backpack and students returned to class.

An officer reviewed the school’s video system and identified a 15-year-old as the person who called in the threat from one of the school’s pay phones. A 17-year-old stood by listening.

Pendleton police cited the boys with disorderly conduct and initiating a false report and booked them into a juvenile facility. Lt. Mark Swanson says the older boy was charged because he made no attempt to stop what was taking place.