The Columbine High School massacre was a school shooting which occurred on April 20, 1999, at Columbine High School in Columbine, an unincorporated area of Jefferson County.  Two senior students, Eric Harris and Dylan Klebold, murdered a total of 12 students and one teacher.  http://history1900s.about.com/od/famouscrimesscandals/a/columbine.htm