Students in one of Long Island's largest school districts are on edge after a threat of violence.Sachem High School East sent letters out to parents saying a threat was found written in the girl's bathroom. The threat stated "I'm going to kill someone in this school" and gave Friday's date. No one specific was mentioned, but Suffolk police say they are treating the threat as an authentic one. School officials say they intend to prosecute the person who is responsible for the message.One bus driver for the school said a significant number of students were not on his bus Friday. He said several parents told him they would be keeping their children home from school because of the threat.