A California teenager has been arrested for threatening in an Instagram post to “take a gun and start a massacre” at his former high school, police said on Monday. Devin Harper, 18, has reportedly been charged with making a criminal threat and is being held on a $50,000 bond. Montebello police said that another teenager who attends Montebello High School saw the Instagram post with the alleged threat from Harper. The mother of the teen reported the incident to police late Friday night and Harper was arrested over the weekend, according to Montebello police. Harper, who was reportedly expelled two years ago from the high school, “told officers that he was unable to access” the Instagram post upon request, police said. The Los Angeles County Sheriff’s Department’s East Los Angeles Station said the department will move to “boost patrol in the areas the station serves” as a precautionary measure.