A 17-year-old is facing possible federal weapons charges. He was arrested near a Las Vegas high school with a loaded MAC-10 machine pistol and silencer in his backpack. The teen was arrested off-campus near Valley High by school police who were called by a passer-by about 1 p.m. Wednesday. Witnesses say the teen had been on school grounds, although he’s not a student at any Las Vegas-area school. It’s the 15th time since August a person with a weapon was arrested at a Clark County school.