Quite a few people here have recommended reading this piece by University of Pennsylvania professor Randall Collins on the psychology of rampage killers. Written before the Newtown murders, it says a lot that seems correct in describing the inner life of a typical such killer when he decides to go about his horrible business and then begins to execute his plans.
I disagree, though, with some of the author’s contentions, in particular the part about such killers having trouble facing people and murdering them. I don’t doubt that some killers do have that difficulty to overcome, but it appears that other killers (especially the more psychopathic among them) have no such difficulty at all. The rampage murderer example Collins goes into most detail about, Michael Carneal, was younger than most (14) and appears to have been less hardened a character than many of the others, and more easily stopped by the sort of domination that Collins describes (read the piece to understand what I mean).
If Adam Lanza was a psychopath, he had hid it well (as some do). Lanza is reported to have worn a mask while performing the killing, however, which does create a small amount of the emotional distance that Collins describes as being necessary in order for most rampage killers to overcome the emotional hesitation that can occur if they look their victims in the face. I think, however, that Lanza’s choice of victim (mostly extremely young children) indicates he may have had no such reluctance to overcome. We may never know, of course, unless authorities manage to reconstruct his computer’s hard drive after he tried to destroy it (that destruction is also unusual, because most of these killers want the world to hear their message of hate and/or pain and the “why” of the subsequent destruction they wreaked).
I also disagree with the part of Collins’ piece where he indicates that the Columbine bombs were secondary; actually, they were a huge part of the plan but they fizzled because the bombmakers made errors, not because they were only interested in firearms. And by the way, Harris seems to have been an excellent example of the sort of psychopath who apparently has no difficulty facing his victims:
[Psychopathy] begins to explain Harris’ unbelievably callous behavior: his ability to shoot his classmates, then stop to taunt them while they writhed in pain, then finish them off. Because psychopaths are guided by such a different thought process than non-psychopathic humans, we tend to find their behavior inexplicable…None of his victims means anything to the psychopath. He recognizes other people only as means to obtain what he desires. Not only does he feel no guilt for destroying their lives, he doesn’t grasp what they feel. The truly hard-core psychopath doesn’t quite comprehend emotions like love or hate or fear, because he has never experienced them directly.
And note this, about bombing vs. shooting for the Columbine murderers:
…[T]he killers, in fact, laughed at petty school shooters. They bragged about dwarfing the carnage of the Oklahoma City bombing and originally scheduled their bloody performance for its anniversary. Klebold boasted on video about inflicting “the most deaths in U.S. history.” Columbine was intended not primarily as a shooting at all, but as a bombing on a massive scale. If they hadn’t been so bad at wiring the timers, the propane bombs they set in the cafeteria would have wiped out 600 people. After those bombs went off, they planned to gun down fleeing survivors. An explosive third act would follow, when their cars, packed with still more bombs, would rip through still more crowds, presumably of survivors, rescue workers, and reporters. The climax would be captured on live television. It wasn’t just “fame” they were after—Agent Fuselier bristles at that trivializing term—they were gunning for devastating infamy on the historical scale of an Attila the Hun. Their vision was to create a nightmare so devastating and apocalyptic that the entire world would shudder at their power.
Lanza probably wasn’t planning to do anywhere near the same damage in terms of numbers (at least it doesn’t appear that way), but he was gunning (literally) for something extraordinary in terms of grief and revulsion, through his choice of the most sympathetic victims possible. It’s hard to avoid the idea that he wanted the entire world to reel back in horror at him.