Posted elsewhere but why not?
Here's an extensive quote:
On April 20, 1999, Eric Harris and Dylan Klebold launched an assault on Columbine High School in Littleton, Colorado, murdering 13 and wounding 23 before turning the guns on themselves. Although it is impossible to know exactly what caused these teens to attack their own classmates and teachers, a number of factors probably were involved. One possible contributing factor is violent video games. Harris and Klebold enjoyed playing the bloody, shoot-'em-up video game Doom, a game licensed by the U.S. military to train soldiers to effectively kill. The Simon Wiesenthal Center, which tracks Internet hate groups, found in its archives a copy of Harris' web site with a version of Doom that he had customized. In his version there are two shooters, each with extra weapons and unlimited ammunition, and the other people in the game can't fight back. For a class project, Harris and Klebold made a videotape that was similar to their customized version of Doom. In the video, Harris and Klebold dress in trench coats, carry guns, and kill school athletes. They acted out their videotaped performance in real life less than a year later. An investigator associated with the Wiesenthal Center said Harris and Klebold were "playing out their game in God mode" (Pooley, 1999, p. 32).
They didn't customize a copy of Risk or make scary looking chess pieces. They used the same software the military apparently uses (?) to train people to kill effectively, so it must be a very realistic simulation.
