RIALTO, Calif. (AP) — Authorities say a 13-year-old boy was arrested after bringing a loaded handgun in his backpack to a Southern California middle school.

The Rialto Unified School District says a safety-intervention officer found the weapon Monday after the student was detained and searched at Kolb Middle School.

Officials didn't say how the officer was made aware of the firearm.

The teen booked at juvenile hall on suspicion of possession of a firearm in a gun-free school zone and possession of a concealed firearm.

Police and the school district are investigating.