ARLINGTON, Wash. – Investigators now say a “homemade explosive device” apparently started a fire in a bathroom at Arlington High School on Tuesday and forced an emergency evacuation.

A 16-year-old student was arrested, and police and agents from the ATF are investigating the incident.

No one was hurt.

The incident started about 8:30 a.m. The school was then placed on modified lockdown as police and fire crews responded.

The students were later evacuated so that police and a Washington State Patrol bomb squad could search all campus buildings for any other devices. None was found.