As Bob Orr reports, Cho, a senior English major at Virginia Tech began his deadly day without warning at West Ambler Johnston Hall. There, inside a dorm room, he point-blank shot and killed a man and a woman.
Sources say Cho then quietly returned to his own dorm, Harper Hall, just a few hundred feet away. And it was there Cho left behind his only explanation for the horror that was about to play out.
Hours after the rampage, sources say investigators found a rambling but threatening letter. Officials decline to call it a suicide note, but in the letter Cho seemed to blame others for his perceived problems, charging that "You made me do this."
"This," as it turned out, would be wholesale slaughter.
Investigators say after stopping at his dorm, Cho then traveled a half mile across campus, chained closed the doors at Norris Hall, and began methodically working his way through four classrooms, shooting students and teachers at will.
Many have multiple gunshot wounds, a clear sign that Cho reloaded perhaps more than once before his rage ended in suicide.
Karan Grewal, who was a suite mate of Cho's, said he saw him just two hours before the first shooting occurred. "He came in, I saw him look normal as usual, no expression on his face, he didn't seem angry or you know sad or anything, just the normal look on his face, just, like the picture," he recalls.
Grewal said Cho barely spoke to his own roommates. "I was shocked. He didn't look like a guy who could really do that. He wasn't angry. He just appeared to be shy, not angry," Grewal explains.
Another student, Aimee Fauser, who lives in Harper Hall, says she and her friends were just lucky not to be in the line of fire. "They're just shocked that it could have happened and that somebody so close did something because he could have come back here between the shootings. And seems like we missed, dodged a bullet there," she explains.
for an interactive gallery of the victims.
Cho, a loner in life, apparently wanted to be anonymous in death. Sources say he carried no identification on him during his killing spree. And the serial numbers on his two handguns had been erased.
But, investigators tell CBS News paperwork in Cho's backpack allowed them to trace one of his guns – a 9mm Glock to a recent purchase at a Roanoke gun store.
Police last night carried out a search of Cho's dorm room and removed letters, papers, and other personal items.
Authorities also searched Cho's home in northern Virginia. His neighbors, like his dorm mates, were stunned to learn that a young man in their midst was behind the Virginia Tech massacre.
"I would never have thought we would have something like that originating here in this town and on this street. This is really shocking. Absolutely," says neighbor Marshall Main.
There were some troubling signs with Cho: students in his writing classes say he often wrote violent scenes they describe as "twisted." He wrote two screenplays dealing with death and revenge – two things that seem to have played out Monday on the Virginia Tech campus.
Police still have no clear motive for the killings. Until the shootings, Cho's only known run-ins with the law were two speeding tickets he picked up in the past three weeks.
Authorities are hard pressed to explain how a man with no criminal past took such an immediate and violent turn.