On 20 April 1999 18-year-old Eric Harris and 17-year-old Dylan Klebold walked into their high school in Columbine, Colorado and, with one act of violence, changed America forever. Harris and Klebold"s plan, which they had been working on for over a year, was to set off homemade bombs, but when those failed to detonate they instead walked through the halls and used the four guns they"d acquired to injure 24 people and kill 13 more before taking their own lives.