The gunman responsible for at least the second of the two Virginia Tech attacks that claimed 33 lives to become the deadliest shooting rampage in U.S. history has been identified as Cho Seung-Hui, a campus student in the United States on a permanent resident visa, Virginia Tech police said Tuesday.

But police are still searching for a motive.

"He was a loner, and we're having difficulty finding information about him," school spokesman Larry Hincker said.

Virginia Tech Police Chief Wendell Flinchum said the shooter was a 23-year-old resident alien who was an undergraduate senior English major. He had a residence in Centreville, Va., but was also living on campus in Harper Hall.

There were two shootings: One shortly after 7 a.m. at the West Ambler Johnston residence hall, which killed two people, and another around 9:15 a.m. at Norris Hall, a classroom building located across campus. Thirty people were killed during that shooting, while another 15 were injured, before Cho shot himself.

List of Victims in Virginia Tech Massacre

"It's certainly reasonable for us to assume Cho was the shooter in both places but we don't have the evidence to take us there at this point in time," said Virginia State Police Superintendent Col. Steve Flaherty said during a press conference Tuesday. "We also have no evidence to indicate there was an accomplice at either event" but officials are still investigating whether the shooter had any help during the day.

"Quite frankly, we have the one chance to get it right," Flaherty said.

Flinchum said a 9mm and 22-caliber handgun was recovered from Norris Hall, where the second shooting took place. Bullets, shell casings and other evidence was examined by the federal Bureau of Alcohol, Tobacco and Firearms. Both weapons are at the ATF's Ammendale Research lab in Maryland, which handles major cases, such as the Beltway sniper attacks.

"Lab results confirmed that one of the two weapons seized in Norris Hall was used in both shootings," Flinchum said.

Processing the scene at Norris Hall has been difficult, Flinchum said, because of the "tremendous chaos and panic" that ensued after the shootings began. Personal effects were strewn about the entire second floor, he said.

Victims were found in at least four classrooms, as well as a stairwell. Flinchum said the gunman was found dead among several victims in one of the classrooms.

Sources told ABC News that after Cho killed the one female and one male at West Ambler Johnston Monday morning, he returned to his own dorm room where he re-armed and left a "disturbing note" before entering Norris Hall on the other side of campus to continue his rampage and kill 30 more before shooting himself.

The Chicago Tribune reported that the note included a rambling list of grievances that railed against "rich kids," "debauchery" and "deceitful charlatans" on campus. The paper also reported that Cho died with the words "Ismail Ax" in red ink on the inside of one of his arms.

Quoting an "investigative source," the newspaper said Cho had shown recent signs of violent, aberrant behavior, including setting a fire in a dorm room and allegedly stalking some women, and that he was taking medication for depression. The Tribune also reported that Cho's family runs a dry cleaning business and he has a sister who attended Princeton University. Cho and his family came to the United States in 1992, when he was 8 years old, and he was a legal permanent resident.

Law enforcement officials told ABCNews.com that Cho bought his first gun, a Glock 9mm handgun, on March 13; they say he bought his second weapon, a 22-caliber handgun, within the last week. The serial numbers on both guns had been filed off, sources said.

ABC News also reported that sections of chain similar to those used to lock the main doors at Norris Hall were also found inside a Virginia Tech dorm.

Flinchum said that a "person of interest" who was an acquaintance of the female victim shot at West Ambler Johnston was stopped off campus and detained for questioning. While he was being questioned, the second shooting took place. Flinchum said they are still looking into the possibility that that person helped Cho.

Flinchum also said there is no evidence yet to connect Monday's shootings to two bomb threats made at the school earlier this month.

Federal law enforcement sources confirmed to FOX News that the address for Cho is 14713 Truitt Farm Dr. in Centreville, Va. Sources familiar with the investigation said a search of the property was done overnight by federal agents, Virginia State Police and Fairfax County Police. Authorities.

'It's Going to be Horrible'

The slayings left people of this once-peaceful mountain town and the university at its heart praying for the victims of the deadliest shooting rampage in U.S. history, struggling to find order in a tragedy of such unspeakable horror it defies reason.

A convocation will be held on campus at 2 p.m. EDT. President Bush and Gov. Tim Kaine planned to attend. About 40,000 people are expected to attend an 8 p.m. vigil Tuesday night.

The school administration is under fire by some who say it didn't inform students sooner about the first shooting, which began about 7:15 a.m. on the fourth floor of West Ambler Johnston. Police were still investigating around 9:15 a.m., when a gunman wielding two handguns and carrying multiple clips of ammunition stormed Norris Hall, on the other side of the 2,600-acre campus. Some students said their first warning came more than two hours after the first shooting, in a vague e-mail at 9:26 a.m.

"I think the university has blood on their hands because of their lack of action after the first incident," said Billy Bason, 18, who lives on the seventh floor of West Ambler Johnston.

Virginia Tech President Charles Steger said the university was trying to notify students who were already on-campus, not those who were commuting in. With 9,000 students on campus, 15,000 or 16,000 more in transit on their way to class, and 7,000 employees, Steger told FOX News, "if you don't do it right and you report misinformation, you've got chaos, and we were trying to manage the incident the best we could."

Steger said authorities believed the first shooting was a domestic, isolated incident confined to the building and that authorities closed down that building and surrounded it with police as a safety precaution. They thought the incident was a murder-suicide.

Asked whether he did everything he could to save lives on campus, Steger said: '"I believe, based on the information we had at the time, we took the appropriate steps."

At least 15 people were hurt in the Norris Hall attack, some seriously. Many found themselves trapped after someone, apparently the shooter, chained and locked Norris Hall doors from the inside.

Students jumped from windows, and students and faculty carried away some of the wounded without waiting for ambulances to arrive.

Classes have been canceled for the rest of the week, and Norris Hall will remain closed for the rest of the semester.

Gregory Walton, a 25-year-old who graduated last year, said he feared the nightmare had just begun. At least one of his friends was among the deceased.

"I knew when the number was so large that I would know at least one person on that list," said Walton, a banquet manager. "I don't want to look at that list. I don't want to.

"It's just, it's going to be horrible, and it's going to get worse before it gets better."

Until Monday, the deadliest shooting in modern U.S. history was in Killeen, Texas, in 1991, when George Hennard plowed his pickup truck into a Luby's Cafeteria and shot 23 people to death, then himself.

Last August, the opening day of classes was canceled when an escaped jail inmate allegedly killed a hospital guard off campus and fled to the Tech area. A sheriff's deputy was killed just off campus. The accused gunman, William Morva, faces capital murder charges.

FOX News' Catherine Herridge, Ian McCaleb and Geraldo Rivera, FOXNews.com's Liza Porteus and The Associated Press contributed to this report.

Click here to read witness accounts of the grisly shootings

Click here to read how a minister is helping Virginia Tech students cope

Click here to read FOXNews.com's interview with one campus professor

Click here for more information on the gunman

Click here to read about the hero professor who was killed trying to help students escape