Va. Tech Shooter a 'Textbook Killer'

Blacksburg, Va., customers watch the NBC Nightly News as they dine in a local restaurant on Wednesday, April 18, 2007. Between his first and second bursts of gunfire, Virginia Tech gunman Cho Seung-Hui mailed a package to NBC that containing photos of him brandishing guns and video of him delivering an angry, profanity laced tirade. (AP Photo/Amy Sancetta) (Amy Sancetta - AP)

However, another expert who has worked with mentally disturbed young criminals suggested that Cho's actions probably had genetic causes.

"This is very different" from someone who was bullied to the breaking point _ Cho was clearly psychotic and delusional, said Dr. Louis Kraus, chief of child and adolescent psychiatry at Chicago's Rush University Medical Center.

"This type of mental illness that this poor man had was not something that was likely precipitated by teasing or bullying," he said. More likely, he said, is that Cho had a biological psychiatric disorder that may have worsened in recent years because of the pressures of college life and his leaving the support of his family.

Randazzo said about the only difference between Cho and the killers studied is he hadn't bragged about the assault in advance, though that may surface later, perhaps in blogs or chat rooms.

Fox, the criminologist, said Cho probably made the decision to go on a killing spree months ago based on his weapon purchase. That would explain why witnesses described him as remarkably calm when he did the shooting.

"There's a lot of scripting that's going on in their heads, a lot of planning. Once they've decided it, there's a certain degree of comfort and satisfaction that they'll be the last to laugh," Fox said.

Fox said there is typically a precipitating event that sets a gunman off. It is not yet known what that was in Cho's case.

"It may not be huge" to normal people, but to Cho "it was the final straw that broke the camel's back," Fox said.

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Associated Press writers Sarah Karush and Seth Borenstein in Washington and Lindsey Tanner in Chicago contributed to this story.