MOUNT VERNON, Wash. -- A 16-year-old boy is in juvenile detention after he allegedly threatened to commit a mass shooting at Mount Vernon High School on the first day of school. Students tipped off their parents after the boy posted warnings of a "Columbine attack" on his Facebook profile Friday. Mount Vernon Police Lieutenant Chris Cammock says students on Facebook took the threats seriously. The boy has a history of contact with police. Officials say he has anger issues and suffers from unpredictable behavior. He was arrested Saturday. The boy is not currently a student at any Mount Vernon school.