"Harris created customized Doom scenarios, adding his own graphics and sounds, and posted them on the Web page for other players to download and use. Before the page was removed by America Online on Wednesday, The Courant downloaded copies of some of the files."
They included a scenario, called "Deathmatching in Bricks!," in which Harris boasted of adding bloody graphics and thanked his "good friend Dylan Klebold for helping me play-test this."
Yup... just another coincidence.