Cho Seung-Hui, a Virginia Tech senior and native of South Korea, has been identified as the gunman in the shootings.
The student who killed 32 people and then himself Monday at Virginia Tech paid $571 for a 9 mm Glock 19 pistol just over a month ago, the owner of Roanoke Firearms told CNN Tuesday.
John Markell said Cho Seung-Hui was very low-key when he purchased the gun and 50 rounds of ammunition with a credit card in an "unremarkable" purchase.
Cho presented three forms of identification and state police conducted an instant background check that probably took about a minute, the store owner said.
Cho did not say why he wanted the gun, Markell said.
A fellow student said the 23-year-old English major had written two plays so "twisted" that his classmates suspected he might become a school shooter.
Ian McFarlane, who said he had class with Cho, called the plays "very graphic" and "extremely disturbing."
McFarlane is an employee of AOL, which has provided the writings to CNN. (Read McFarlane's blog and the two playsexternal link)
"It was like something out of a nightmare," McFarlane wrote in a blog. "The plays had really twisted, macabre violence that used weapons I wouldn't have even thought of.
"Before Cho got to class that day, we students were talking to each other with serious worry about whether he could be a school shooter."
A university official also said that Cho scribed writings so "disturbing" they were sent to administrators, a university official said Tuesday.
The official did not provide details about the writings, which first came to the attention of faculty in the English department, but said they were passed on to the department chairwoman and university administrators.
Cho left a long and vitriolic note in his dorm room, law enforcement sources told ABC News. It contained an explanation of his actions and states, "You caused me to do this," ABC News reported.
It also railed against "rich kids," "debauchery" and "deceitful charlatans" on campus, according to the Chicago Tribune.
University officials said they were still trying to determine whether Cho was responsible for a shooting earlier Monday that left two dead at a dormitory.
However, Virginia Tech Police Chief Wendell Flinchum said ballistics tests show that one of the two guns recovered at Norris Hall was used at Norris and at the dorm, both located on the 26,000-student campus.
Authorities are still investigating whether Cho had any accomplices in planning or executing Monday's rampage, Col. Steven Flaherty of the Virginia State Police said.
"It certainly is reasonable for us to assume that Cho was the shooter in both places, but we don't have the evidence to take us there at this particular point in time," Flaherty said.
Cho, a 23-year-old South Korean and resident alien, was an English major who lived at the university's Harper Hall, Flinchum said.
"He was a loner, and we're having difficulty finding information about him," said Larry Hincker, associate vice president for university relations.
Cho came to the United States in 1992, through Detroit, Michigan, a department of Homeland Security official said. He had lawful permanent residence, via his parents, and renewed his green card in October 2003, the official said.
His residence was listed as Centreville, Virginia, a suburb of Washington, D.C.
The university and police are still in the process of releasing the names of those killed in Monday's shootings.
"What went on during that incident certainly caused tremendous chaos and panic in Norris Hall," Flaherty said, describing how victims were found in four classrooms and in the stairwell of the school's engineering science and mechanics building.
Doctor recalls 'amazing' injuries
A doctor at a Blacksburg hospital described the injuries he saw Monday as "amazing" and the shooter as "brutal."
"There wasn't a shooting victim that didn't have less than three bullet wounds in them," said Dr. Joseph Cacioppo of Montgomery Regional Hospital.
A source familiar with the investigation said the weapons found at Norris were a Walther .22-caliber semi-automatic and a 9 mm Glock -- both with the serial numbers filed off.
As questions continued to arise about how police reacted to the first shooting at the dorm, university President Charles Steger on Tuesday defended the response, saying police believed it to be "a domestic fight, perhaps a murder-suicide" that was contained to one dorm room.
Police cordoned off the 895-student West Ambler Johnston dorm and all residents were told about the shooting as police looked for witnesses, Steger said.
Authorities were still investigating what they believed was an "isolated incident" when the slaughter occurred at Norris Hall.
"I don't think anyone could have predicted that another event was going to take place two hours later," Steger said, adding that it would've been difficult to warn every student because most were off campus at the time.
Steger told reporters Monday that when police responded to Norris Hall they found the front doors chained shut. The gunfire had stopped by the time they reached the second floor, he said.
The gunman killed 31 people, including himself, and wounded 15 in Norris Hall classrooms.
Student heard clip drop to ground
Zach Petkewicz was in class when the shooting at Norris began and "everyone went into a frenzy, a panic." Petkewicz was hiding behind a podium when he realized there was nothing preventing the shooter from entering the classroom and barked to his classmates, "We need to barricade this door."
Two students joined him in throwing tables against the door and wedging their weight behind them, just as the gunman cracked open the door.
When the students slammed the door in his face, "he backed up and shot twice into the middle of the door thinking we were up against it," Petkewicz said.
"I was up against the side holding this desk up against there and I just heard his clip drop to the ground and he reloaded, and I thought he was coming back for a second round, to try and get his way in there," he said. "He didn't say a word, and he just turned and kept firing down the hall and didn't try to get back in."
As of midday Tuesday, officials were still releasing the names of those killed, which include a marching band member from Georgia and an Israeli Holocaust survivor who headed the engineering and science department.
Classes have been canceled for the rest of the week, and Norris Hall will be closed for the remainder of the semester, Steger said. Emily Alderman, who works at a clothing store near campus, said students were sending out instant messages urging one another to wear their Virginia Tech Hokie gear in a sign of unity.
The rest of spring football season also has been canceled, the university announced.
There have been two bomb threats at the university this month, the latest of which came Friday. Flinchum said Tuesday they were unrelated to the shootings.
Last August, the first day of class was cut short at Virginia Tech by a manhunt for an escaped prisoner accused of killing a Blacksburg hospital security guard and a sheriff's deputy.
Before Monday, the deadliest mass shooting in the United States occurred in 1991, when George Hennard drove a pickup truck into a Killeen, Texas, cafeteria and fatally shot 23 people, before shooting and killing himself.
Source: CNN.com