According to a statement from the Chino Hills Police Department, a "concerned citizen," who wished to remain anonymous, tipped them off Thursday about a video the boy made in which he rapped about getting in fights with other students and shooting a specific staff member at the school.
After investigating, police notified school staff, then went to the boy's home where they discovered the family had guns in a locked safe, the statement said. He was then arrested and booked into juvenile detention.