A chilling picture emerged Tuesday of Cho Seung-Hui - a 23-year-old senior majoring in English - a day after the bloodbath that left 33 people dead, including Cho, who killed himself as police closed in.
News reports said that he may have been taking medication for depression and that he was becoming increasingly violent and erratic.
Despite the many warning signs that came to light in the bloody aftermath, police and university officials offered no clues as to exactly what set Cho off on the deadliest shooting rampage in modern U.S. history.
"He was a loner, and we're having difficulty finding information about him," school spokesman Larry Hincker said.
A student who attended Virginia Tech last fall provided obscenity- and violence-laced screenplays that he said Cho wrote as part of a playwriting class they both took.
One was about a fight between a stepson and his stepfather, and involved throwing of hammers and attacks with a chainsaw. Another was about students fantasizing about stalking and killing a teacher who sexually molested them.
"When we read Cho's plays, it was like something out of a nightmare. The plays had really twisted, macabre violence that used weapons I wouldn't have even thought of," former classmate Ian MacFarlane, now an AOL employee, wrote in a blog posted on an AOL Web site. He said he and other students "were talking to each other with serious worry about whether he could be a school shooter."
"We always joked we were just waiting for him to do something, waiting to hear about something he did," said another classmate, Stephanie Derry. "But when I got the call it was Cho who had done this, I started crying, bawling."
Professor Carolyn Rude, chairwoman of the university's English department, said Cho's writing was so disturbing that he had been referred to the university's counseling service.
"Sometimes, in creative writing, people reveal things and you never know if it's creative or if they're describing things, if they're imagining things or just how real it might be," Rude said. "But we're all alert to not ignore things like this."
She said she did not know when he was referred for counseling, or what the outcome was. Rude refused to release any of his writings or his grades, citing privacy laws. The counseling service refused to comment.
Cho - who arrived in the United States as boy from South Korea in 1992 and was raised in suburban Washington, D.C., where his parents worked at a dry cleaners - left a note that was found after the bloodbath.
A law enforcement official who read Cho's note described it Tuesday as a typed, eight-page rant against rich kids and religion. The official spoke on condition of anonymity because he was not authorized to speak to the media.
"You caused me to do this," the official quoted the note as saying.
Cho indicated in his letter that the end was near and that there was a deed to be done, the official said. He also expressed disappointment in his own religion, and made several references to Christianity, the official said.
The official said the letter was either found in Cho's dorm room or in his backpack. The backpack was found in the hallway of the classroom building where the shootings happened, and contained several rounds of ammunition, the official said.
Col. Steve Flaherty, superintendent of the Virginia State Police, said authorities were going through a considerable number of writings.
Citing unidentified sources, the Chicago Tribune reported Cho had recently set a fire in a dorm room and had stalked some women.
Monday's rampage consisted of two attacks, more than two hours apart - first at a dormitory, where two people were killed, then inside a classroom building, where 31 people, including Cho, died. Two handguns - a 9 mm and a .22-caliber - were found in the classroom building.
The Washington Post quoted law enforcement sources as saying Cho died with the words "Ismail Ax" in red ink on one of his arms, but they were not sure what that meant.
According to court papers, police found a "bomb threat" note - directed at engineering school buildings - near the victims in the classroom building. In the past three weeks, Virginia Tech was hit with two other bomb threats. Investigators have not connected those earlier threats to Cho.
Cho graduated from Westfield High School in Chantilly, Va., in 2003. His family lived in an off-white, two-story townhouse in Centreville, Va.
At least one of those killed in the rampage, Reema Samaha, graduated from Westfield High in 2006. But there was no immediate word from authorities on whether Cho knew the young woman and singled her out.
"He was very quiet, always by himself," neighbor Abdul Shash said. Shash said Cho spent a lot of his free time playing basketball and would not respond if someone greeted him.
Classmates painted a similar picture. Some said that on the first day of a British literature class last year, the 30 or so students went around and introduced themselves. When it was Cho's turn, he didn't speak.
On the sign-in sheet where everyone else had written their names, Cho had written a question mark. "Is your name, â€˜Question mark?'" classmate Julie Poole recalled the professor asking. The young man offered little response.
Cho spent much of that class sitting in the back of the room, wearing a hat and seldom participating. In a small department, Cho distinguished himself for being anonymous. "He didn't reach out to anyone. He never talked," Poole said.
"We just really knew him as the question mark kid," Poole said.
One law enforcement official said Cho's backpack contained a receipt for a March purchase of a Glock 9 mm pistol. Cho held a green card, meaning he was a legal, permanent resident. That meant he was eligible to buy a handgun unless he had been convicted of a felony.
Roanoke Firearms owner John Markell said his shop sold the Glock and a box of practice ammo to Cho 36 days ago for $571.
"He was a nice, clean-cut college kid. We won't sell a gun if we have any idea at all that a purchase is suspicious," Markell said.
Investigators stopped short of saying Cho carried out both attacks. But State Police ballistics tests showed one gun was used in both.
And two law enforcement officials, speaking on condition of anonymity because the information had not been announced, said Cho's fingerprints were on both guns, whose serial numbers had been filed off.
Gov. Tim Kaine said he will appoint a panel at the university's request to review authorities' handling of the disaster. Parents and students bitterly complained that the university should have locked down the campus immediately after the first burst of gunfire and did not do enough to warn people.
Kaine warned against making snap judgments and said he had "nothing but loathing" for those who take the tragedy and "make it their political hobby horse to ride."
On Tuesday afternoon, thousands of people gathered in the basketball arena for a memorial service for the victims, with an overflow crowd of thousands watching on a jumbo TV screen in the football stadium. President Bush and the first lady attended.
"As you draw closer to your families in the coming days, I ask you to reach out to those who ache for sons and daughters who are never coming home," Bush said.
Virginia Tech President Charles Steger received a 30-second standing ovation, despite the criticism of the school administration.
With classes canceled for the rest of the week, many students left town in a hurry, lugging pillows, sleeping bags and backpacks down the sidewalks.
Jessie Ferguson, 19, a freshman from Arlington, headed for her car with tears streaming down her cheeks.
"I'm still kind of shaky," she said. "I had to pump myself up just to kind of come out of the building. I was going to come out, but it took a little bit of â€˜OK, it's going to be all right. There's lots of cops around.'"
She added: "I just don't want to be on campus."
Stories of heroism and ingenuity emerged Tuesday.
Liviu Librescu, an Israeli engineering and math lecturer, was killed after he was said to have protected his students' lives by blocking the doorway of his classroom from the gunman.
And one student, an Eagle Scout, probably saved his own life by using an electrical cord as a tourniquet around his bleeding thigh, a doctor reported.
The near-death ordeal of senior Kevin Sterne was captured in a photograph that played on newspaper front pages across the country.
Sterne was among the dozens of students shot in Norris Hall classrooms Monday.
He was in stable condition Tuesday, and doctors credited his quick thinking. Doctors said Sterne kept enough cool to fashion a tourniquet from an electrical cord after a bullet tore a inch-long gash through the femoral artery of his right leg.
"The patient that I took care of was an incredible guy," said Dr. David Stoeckle, chief of surgery at Montgomery Regional Hospital. "He was bleeding significantly ... he knew he was bleeding to death."
Emergency workers later applied a second tourniquet to the leg before racing him to the hospital for immediate surgery, Stoeckle said. The surgeon did not identify Sterne by name, but his parents told reporters Tuesday their 6-foot-2 son was the student in the photograph.
Sterne still has a bullet fragment in his right femur, and doctors haven't determined whether they need to remove it, his parents said.
On Tuesday night as darkness fell, thousands of Virginia Tech students, faculty and area residents poured into the center of campus to grieve together. They held thousands of candles aloft as speakers urged them to find solace in one another.
Most of the vigil was devoted to silence and quiet reflection. As the silence spread across the grassy bowl of the drill field, a pair of trumpets began to play taps. A few in the crowd began to sing Amazing Grace. "We will move on from this. But it will take the strength of each other to do that," said Zenobia Hikes, vice president for student affairs. "We want the world to know we are Virginia Tech, we will recover, we will survive with your prayers."
(AP) Associated Press writers Stephen Manning in Centreville, Va.; Matt Barakat in Richmond, Va.; Lara Jakes Jordan and Beverley Lumpkin in Washington; and Vicki Smith, Sue Lindsey, Adam Geller and Justin Pope in Blacksburg contributed to this report. AP-CS-04-17-07 2148EDT