Nothing in Cho's "message" to NBC News dissuades me from my initial impression that he was the stereotype of the mass murderer. It's all there: a rough early childhood (he grew up poor with his family in South Korea until they moved to Northern Virginia in search of a better life), a hatred toward the world for unspecified "wrongs" they committed against him, a delusion of grandeur (he compares himself to Jesus Christ) and the images of him putting a gun to his head. This was a deeply disturbed young man bent on destroying himself and whoever was in his path. It's not clear yet whether or not he had specific targets in his rampage. But since he seemed to see all people around him as cruel to him, it's likely that he just wanted to take as many people as he could down with him.
As for whether he could have been stopped, with warning signs such as his blood-drenched writings and threatening e-mails to female classmates, and concerns from acquaintances that he was suicidal, I doubt it. The school could have taken more drastic disciplinary action, even kicked him out of the school, but I think all that would have done was fuel his rage further. There are too many stories of men fired from jobs who come back with guns. Cho had a plan, which he worked on well in advance of April 16, and that plan was a dramatic suicide including the deaths of others. If it hadn't been Virginia Tech, he would have lashed out somewhere else, or in another way. Unless he was in prison, I don't think he could have been stopped. And what is it about hindsight being 20/20? Eric Harris and Dylan Klebold, the Columbine killers (who Cho mentions as "martyrs" in his message), supposedly left all kinds of warning signs that were revealed after the fact. Cho was clearly disturbed, but no one could have predicted that he would have lashed out quite like this.