According to the 1968 Federal Gun Control Act, no one can buy a gun who's been "adjudicated as a mental defective or ... committed to any mental institution," reports CBS News correspondent Wyatt Andrews.
In December 2005, a Virginia justice directed Cho to undergo "court-ordered outpatient treatments," which was not a commitment to an institution, so Cho's name wasn't sent to the federal data base used for gun purchase background checks.
Gov. Timothy M. Kaine now wants the state to report all patients ordered into therapy, adds Andrews.
On the Virginia Tech campus, classes are back in session this week, with counselors available for students and staff who needed to talk.
Joe Merola needed them Monday after trying to give his students a lecture on an equation explaining the voltage in batteries. 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 a week after Cho killed two people in a dormitory and gunned down 30 in a classroom building before killing himself.
Students and staff paused for moments of silence Monday at the times Cho opened fire. The tributes included an emotional ceremony with a bell tolling 33 times and students and faculty released white balloons for each victim. After a few chants of "Let's Go, Hokies," the students and professors headed off to class.
Queen Elizabeth II also plans to 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 Tuesday. 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.
Two of the students wounded during the shootings remained hospitalized Tuesday, one in stable condition and another in serious condition.
Hilary Strollo, 19, was among those back at home, recovering from gunshots to her head and abdomen. She was in French class when the gunman started firing. One bullet struck her liver.
"Hilary is very lucky," her father, Dr. Patrick Strollo, said outside the family's home north of Pittsburgh. "She's a normal 19-year-old and she's looking forward to all the things 19-year-olds look forward to."
Karan Grewal, one of Cho's suitemates, said he was surprised to find the classrooms almost full Monday.
"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."
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.
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 to be used for classes again, Provost Mark McNamee said. Workers were putting up a chain-link fence around it Monday, and classes that had been held there were relocated.
Merola, a 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.
"We could use a lot more hugs."