A 13-year-old Indiana boy was arrested Friday after investigators determined threats he made on Snapchat to shoot up a dance at his school "were legitimate," police said.The Lafayette Police Department was notified of the Tecumseh Junior High School student's threats on the picture-taking app at 12:14 a.m., according to a news release.Investigators contacted Snapchat for help locating the teen, Lt. Justin Hartman told NBC News.He was scheduled to appear in court before a judge sometime Friday.“However, there will be an increased security presence for the various activities this evening near Jefferson High School and Tecumseh Middle School.”The dance at Tecumseh, a school with 1,102 students in seventh and eighth grade, will go on as planned, according to the school district."