A Somerset County high school student was arrested Monday on accusations he threatened to shoot up the school he attends, officials said. Shortly after 12 p.m. on May 25, Watchung Hills Regional High School received a call from a person who said they were armed with weapons in a school bathroom and were going to “shoot up the school at the next bell,” according to a joint statement from the Somerset County Prosecutor’s Office and the Warren Township Police Department. Multiple officers were called to the school as it was placed under lockdown and the entire building and they searched the prope…