Police arrested a student after he allegedly brought an AR-15 and ammunition to a Phoenix high school on Friday, authorities said.

The student is facing “serious felony charges” after allegedly bringing the semi-automatic rifle — the weapon behind a dozen of the 21 deadliest mass shootings in the U.S. since 2006 — to Bostrom High School, where he was arrested in the main office around 1 p.m. on Friday, according to a news release from the Phoenix Police Department.

Authorities also allegedly found more ammunition in the student’s backpack and lunch box, according to the police department.