The Pasadena Fire Department responded to a fire alarm at Wilson Middle School Tuesday night about 2:18 a.m., authorities said.
Fire crews located the origin of smoke in the girls locker room and found a locker with charred clothing and a recently extinguished fire, a spokesperson said.
A second pile of clothing was located nearby and a window and door were reportedly found propped open to the secured facility. Additionally, a fire extinguisher was found to be missing from the scene, authorities said.
Pasadena Unified spokesperson Adam Wolfson acknowledged the incident, saying District officials have video footage of three intruders setting a fire which caused almost no physical damage.
Both Pasadena police detectives and Fire Dept. arson investigators are investigating the incident.