Who was Seung-hui Cho? What led the troubled 23-year-old to snap and go on a shooting spree?
It is a question that haunts those who knew him.
In the disturbing note he left behind that said "You made me do this," Cho went on a rant against "rich kids," "debauchery" and "deceitful charlatans" on campus.
His dormitory roommates, Joseph Aust and Karan Grewal, steered clear of Cho when they lived with him. They said Cho was quiet and didn't interact with them.
"He pretty much never talked at all," Aust said. "I tried to make conversation with him earlier in the year. … He gave one-word answers. He pretty much never looked me in the eye."
Though Cho's behavior was always strange, Aust said he noticed some changes in recent weeks.
"The last couple weeks [he] was getting up at 6 [in the morning] or even 5:30," Aust said. "And a couple of days ago, he actually got back to the room at about 2 in the afternoon and slept until 5 the next day."
Two roommates from a previous year told CNN in an interview Tuesday night that Cho "stalked" three different women and that one of them was so "freaked out by his behavior" that she called the police on him.
Cho also had an imaginary girlfriend named "Jelly," who was a supermodel, said those roommates.
Cho seemed to take solace from music, which his roommates said he obsessively downloaded from the Internet. One of his favorites was the song "Shine" by Collective Soul, which he played over and over.
He even scribbled some of the song's lyrics on the wall, said his roommates, writing: "Teach me how to speak; Teach me how to share; Teach me where to go."
Trey Perkins, a student who saw Cho during the shooting spree, said it was unreal, "being that close to a monster."
"I mean, someone that would kill 30 people just without even the slightest emotion on their face," Perkins said.
Cho was a senior English major who wrote twisted, angry poems and plays that now seem like warning signs that he could snap.
One troubling play he wrote, "Richard McBeef," was about a 13-year-old who accuses his stepfather of trying to molest him. The teenage character in the play smiles as he throw darts at his stepfather's picture, saying, "I hate him. Must kill Dick. Dick must die. You don't think I can kill you?"
Lucinda Roy, co-chair of the Virginia Tech English Department, said Cho's plays were so disturbing that he made other students uncomfortable. He was eventually asked to drop the class.
"He was so distant and lonely, it was almost like talking to a hole, as though he wasn't really there most of the time," Roy said on "Good Morning America."
"He … said to me once he was lonely and didn't have friends," Roy said.
Pamela Blake, a psychiatrist at Memorial Hermann NW Hospital in Houston, calls Cho's writing chilling, scary and disturbing.
"They're a description or a manifestation of his aggressive feelings," she said.
In another play, Cho writes about three teenagers who sneak into a casino and discuss how they want to end the life of one of their teachers.
"I'd like to kill him," Cho wrote. "He lives off of the misery he inflicts on us, giving me an after school detention and … raping me for making a harmless joke. I want to kill him."
Former FBI agent Brad Garrett said Cho's anger and aggressiveness had likely been building up for a long time.
"He is so dehumanized to all of us," Garrett said. "So what he is shooting is all anger and rage, big-time narcissism."
Cho's roommates said they didn't think they could have done anything differently to reach out to Cho and change what had happened.
"After the freshman year, you don't probe too much if people don't actively converse with you," roommate Grewal said . "I think I'd be scared if I tried any harder. I could have made him angry and act violently towards me."