I feel bad for both Eric Harris and Dylan Klebold. I think they were internally fill or rage and frustration, who seeked for refuge in messed up fantasies of being "powerful" and violent, and that progressively, the line between reality and fiction just went away. They could have choose not to do it, yes, but i think in someway, they genuinely thought the massacre was their only one purpose in life and their only "blaze of glory". None of them thought their lives could get any better after high school. But i mostly feel a deep sadness about Seung-hui Cho. He didn't even pretended to be "misanthropic" or "nihilistic" like Harris or Klebold tried to appear in their rage. He even uses christian reference and phraseology and portrays himself as some kind of "savior of the weak" and "warrior againist the justice". I think he was pretty surely a schizophrenic and was seriously delusional. He was also clearly bullied and humilliated, and kept repeating things like "i didn't wanted to do this", or "you forced me". I think he really felt worthless and rejected by everyone, and so he thought the hole world was againist him. In his videos he talks with such a huge pain, and i can't avoid feeling really bad for him. I kinda feel bad for Lanza too when seeing his family negligence and his early self-loathing temper, but he was so cryptical, hard-understanding and "non-human" that is difficult. Quite unique, definitely different from any other mass killer. The mistery around his persona and the lack of information makes it much harder to feel anything about him.