But he couldn't get through it. Looking out at 100 students and a Virginia Tech sweat shirt he had placed on a seat to honor a student who was wounded, he broke down.

"I lost it halfway through class," Merola said. "I burst into tears and had to turn it over to the counselors."

It was a common sentiment around campus as grieving students returned Monday, one week after Seung-Hui Cho killed 32 people before turning the gun on himself.

Students and staff paused for moments of silence at the times when Cho opened fire in two campus buildings more than two hours apart.

Next month, Queen Elizabeth II also will pay tribute to the shooting victims when she visits Virginia for the 400th anniversary of the first permanent English settlement in the New World, Buckingham Palace said today. There was no immediate indication what sort of ceremony will be held, but a visit to the campus was ruled out, a palace spokeswoman said on condition of anonymity in line with royal rules.

"As the queen is visiting so shortly after the tragedy, it is important that it be recognized," the spokeswoman said in London.

Monday's tributes included an emotional ceremony in which a man in a Virginia Tech hat rang a bell 33 times and students and faculty released white balloons for each victim.

Then 1,000 balloons were released in the school colors — maroon and orange — as people stood in silence, hesitant to let the moment pass.

After a few chants of "Let's Go, Hokies," they headed off to class.

Karan Grewal, one of the gunman's suitemates this year, went to two classes Monday, intermediate accounting and taxes. He was surprised to find the classrooms almost full.

"Both of the teachers I went to, they kind of teared up at the beginning of the class when they started talking about what happened," he said. "A couple of students did, too. Then we all got together and kind of took care of business."

Paul Deyerle attended three classes, and he took comfort in the fact that his abnormal-psychology teacher kept choking up during class. Students hugged and shed tears themselves.

"Ordinarily, professors are so stoic," he said. "It was nice to see someone sharing what I was feeling."

Monday was the first time since the shootings that Andrea Falletti had been near the memorial to the victims in front of Burruss Hall, which served as a triage center for those shot at nearby Norris Hall. Faint, brownish bloodstains still marred the sidewalk.

"Every day, you wake up and you don't know what you should do. Everyone's like, 'Should we do something? Should we try to have fun?"' said Falletti, a 21-year-old senior. "You almost feel guilty smiling in Blacksburg."

Official said as many as 90 percent of Virginia Tech students returned to campus, and added that class attendance Monday hovered around 75 percent.

Provost Mark McNamee reported at least one sign of normalcy: "The same students who sit in the last row are still nodding off in class."

The return to class came as investigators worked tirelessly to figure out what motivated Cho and whether he had any contact or connection to his victims.

Police have pulled from the university computer server all e-mails to and from Cho, as well as e-mails to and from his first victim, Emily Hilscher, according to court documents filed Monday. Police also recovered other e-mail logs and Cho's personal cell phone records.

Investigators are also trying to piece together the details of Cho's final months, as he prepared for what ended up being the deadliest mass shooting in modern U.S. history.

Students only have two weeks of school left — classes this week and a week of finals. Virginia Tech is allowing students to drop classes without penalty or accept their current grades. That means many students can pick and choose which classes to attend, depending on whether they need to improve their grades.

"I know that a lot of kids were moving out last night and today to go home for the semester. A lot of them had really good grades and thought that it made no sense to stay here," said student Meghan Brady, who said she loves Virginia Tech so much that she couldn't imagine heading home for the summer.

Two students remained hospitalized, one in stable condition and another in serious condition.

The killings did not appear to be affecting the number of prospective students, who must decide by May 1 whether they will enroll this fall.

University officials said they have not yet decided on the future of Norris Hall, the classroom and office building where most victims were killed. But it is unlikely that Norris will be used for classes again, McNamee said.

Workers were putting up a chain-link fence around it Monday, and classes that had been held there have been relocated.

Merola, the chemistry professor, said he finally got around to his lecture on the Nernst equation toward the end of class.

At the end, the students "started lining up and every one of them gave me a hug. That was unexpected for me," he said.