A court-ordered mental health evaluation of Virginia Tech mass-murderer Seung-Hui Cho in December 2005 found him "mentally ill and in need of hospitalization" and "an imminent danger to self and others." But that never showed up in computer records when he went to buy his gun.
"We ran a state police background check," said Roanoke Firearms store owner John Markell, whose store sold Cho a Glock 19 handgun. "It came back clean."
Federal law is fairly clear. According to the "Brady Handgun Violence Prevention Act'' that became law in 1993, anyone who "[h]as been adjudicated as a mental defective or committed to a mental institution" is prohibiting from purchasing a firearm.
The definition of a "mental defective" includes anyone whom "a court, board, commission, or other lawful authority" has determined to be "a danger to himself or other" because of "marked subnormal intelligence, or mental illness, incompetency, condition, or disease."
Cho might seem to qualify as a "mental defective" by that definition, but FBI spokesman Steve Fischer said it's up to each state to determine who qualifies a "mental defective." And Virginia chooses to draw its lines in a way that didn't include Cho, even though he was found "mentally ill" and "a danger to self and others."
That's because in December 2005, Special Justice Paul Barnett ultimately decided Cho only needed outpatient care for his mental illness, not inpatient care, which would have triggered notification to law enforcement, which then should have been included in the National Instant Check System.
"Short of the involuntary admission to a hospital, no such report and no such law affects them," Barnett told ABC News.
Kristin Rand of the gun control group the Violence Policy Center said Virginia is skirting federal law by applying too narrow a definition of mental problems.
"I think it's pretty clear that Mr. Cho should have been prohibited from buying these guns," Rand said. "He had been clearly adjudicated as a mental defective, as unpleasant as that language might be."
Rand said Virginia -- and other states -- need to expand their definition of "mentally defective.
But policymakers who have pushed this issue before have met with resistance from mental health care professionals, who say such an expansion would increase the stigma for those with mental problems and scare many away from seeking help.
"It further underscores this notion that once you have a diagnosis of mental illness, you never get better, you never get over it," said David L. Shern, president and CEO of the National Mental Health Association. "And that just doesn't comport with the facts."
All of which means, a few weeks ago, when Cho filled out this federal gun form and checked that he had never "been adjudicated mentally defective," according to Virginia law he was not lying.
ABC News' Terry Moran, Ellen Davis and Lisa Chinn contributed to this report.