According to the writings found in Eric Harris’ and Dylan Klebold’s diaries they were big fans of Doom. They killed 13 people before taking their own lives in the Columbine High School shootings in 1999.
The following material related to Doom was found in the diaries:
Regarding his love for Doom:
“My love for a computer game called Doom. Doom is such a big part of my life and no one I know can recreate environments in Doom as good as me. I know almost anything these is to know about that game, so I believe that separates me from the rest of the world… Doom is so burned into my head my thoughts usually have something to do with the game… the fact is I love that game and if others tell me, “hey it’s just a game” I say “hey, I don’t care.”
A year before the massacre:
“…everyone should be put to a test. an Ultimate Doom test. See who (unreadable) an environment using only smarts and military skills… Put them in a Doom world, no authority, no refuge, no BS copout excuses. If you can’t figure out the area of a triangle or what (unreadable) means, you die! If you can’t take down a demon w/a chainsaw or a hell prince w/a shotgun, you die!”
On the planned shootings:
“It’ll be like the LA riots, the Oklahoma bombing, WWII, Vietnam, Duke and Doom all mixed together. … I want to leave a lasting impression on the world.”
He also wrote a letter to id software which can be found here.