Roanoke Firearms owner John Markell shows a Glock 9 mm pistol that is similar to the one sold in his Virginia gun shop to the Virginia Tech gunman weeks before Monday's shootings. Federal rules bar the sale of guns to individuals who have been "adjudicated mentally defective." DON PETERSEN | Associated Press

But it was unclear Thursday whether anybody had an obligation to inform federal authorities about Cho's mental status because of loopholes in the law that governs background checks.

Cho purchased two handguns in February and March, and was subject to federal and state background checks both times. The checks turned up no problems, despite a judge's finding in December 2005 that Cho "presents an imminent danger to himself as a result of mental illness."

"On the face of it, he should have been blocked under federal law," said Denis Henigan, legal director of the Brady Center to Prevent Gun Violence.

The 23-year-old South Korean immigrant was evaluated by a psychiatric hospital after he was accused of stalking two women and photographing female students in class with his cell phone. And his violence-filled writings were so disturbing he was removed from one class, and professors begged him to get counseling.

The finding by Special Justice Paul M. Barnett is almost identical to federal regulations from the Bureau of Alcohol, Tobacco, Firearms and Explosives. Those rules bar the sale of guns to individuals who have been "adjudicated mentally defective."

The definition outlined in the regulations is "a determination by a court ... or other lawful authority that a person as a result of marked subnormal intelligence, or mental illness ... is a danger to himself or to others."

Virginia State Police send information on prohibited buyers to the federal government. They maintain that the sale was legal under state law and would have been barred only if the justice had committed Cho to a psychiatric hospital. Barnett ordered outpatient treatment instead.

The Virginia attorney general's office declined to discuss the application of gun laws to Cho's case. Barnett also declined to comment.

The state uses a slightly different standard than the federal government, barring sales to individuals who have been judged "mentally incapacitated."

But the lack of a commitment order does not change the fact that Cho should have been a prohibited buyer under federal law, said George Burke, a spokesman for Democratic Rep. Carolyn McCarthy of New York. She has sponsored legislation since 2002 that would close loopholes in the national background check system for gun purchases.

Burke said there are millions of criminal and mental-health records that are not accessible to the National Instant Criminal Background Check System, mostly because state and local governments lack the money to submit the records.

Initially states were required to provide all relevant information to federal authorities when the instant background checks were enacted, but a U.S. Supreme Court ruling relieved them of that obligation.

"The law is very confused about this," said Richard Bonnie, a professor of law and psychiatry at the University of Virginia who also heads a state commission on mental-health reform. "The source of the confusion is the relation between federal and state law."

Also Thursday, the owner of an Internet gun store based in Green Bay, Wis., told The Associated Press that one of the weapons used in the Virginia Tech shootings was purchased from his Web site.

Eric Thompson, who runs www.thegunsource.com, said the Walther .22-caliber handgun was then shipped to a Virginia pawnbroker so Cho could pick it up.

"I just feel absolutely terrible that this tragedy even happened in the first place," Thompson said. "I have three children in the first place, and it's just an absolute tragedy."