From the Federal Bureau of Investigation's (FBI) website: "On April 20, 1999, Eric Davis Harris (1981-1999) and Dylan Bennet Klebold (1981-1999) killed 12 students and one teacher at Columbine High School in Littleton, Colorado before committing suicide. The tragedy sparked national debates about school safety. The FBI assisted local law enforcement by investigating additional threats and Internet leads, conducting witness interviews, and processing physical evidence. The FBI's file details the initial investigation and contains witness interviews between April 21, 1999 and May 5, 1999."
Federal Bureau of Investigation: http://www.fbi.gov/