Police arrested a 16-year-old boy on Monday after receiving a tip that he was allegedly recruiting other students to join in on a “mass shooting and/or bombing” at a California high school, Berkeley police said Wednesday. Authorities said they found parts of explosives, assault rifles, knives and other items that could have been used to build weapons while searching the boy’s home. He was arrested and charged with threatening to commit a crime which will result in death or great bodily injury and possessing destructive device materials after turning himself into the police Monday. Because he’s a minor, the boy’s name was not released, and it’s unclear whether he attended his target, Berkeley High School. The school district’s superintendent, Brent Stephens, informed the community of the investigation and subsequent arrest in a letter Wednesday, thanking whoever submitted the tip to police.