Major gaps abound in U.S. laws aimed at preventing violent criminals from getting their hands on firearms, experts at a policy summit on gun laws said Monday.

"The background check system is only as good as the records that inform these decisions," said Janey Rountree of the Mayors Against Illegal Guns, referring to the system that requires those purchasing guns from licensed dealers to submit to a criminal background check.

The debate over gun control came to a boiling point last month when a deranged gunman shot dead 20 students in a shooting spree at an elementary school in the state of Connecticut. The incident, which shocked nations worldwide, spurred the White House to call for more gun regulation.

President Barack Obama said Monday he would support several measures on gun control, including better background checks.

Referencing the 2007 shootings at Virginia Tech, Rountree noted that shooter Seung-Hui Cho was deemed mentally ill by a Virginia court that failed to forward court records to the national background check system.

As a result, the deranged gunman passed several national and state background checks, and was able to purchase handguns and murder 32 people in one of the worst mass murders in U.S. history, said Rountree at the summit at Johns Hopkins University in Baltimore, Maryland.

The killing spree caused lawmakers to pass bipartisan legislation encouraging states to forward records to the national background check system, although Congress cannot by law force states to do so.

Despite the legislation, there remain 19 states reporting fewer than 200 records into the national background check system, Rountree said, referencing an investigation by her organization based on data from the Federal Bureau of Investigation.

"That means that there are 19 states where anyone who would be disqualified from buying a gun because of their mental health history, will pass a background check," she said.

She added that state privacy laws are a major barrier, but emphasized that only law enforcement officers running background checks on would-be gun buyers have access to that information once submitted to the national instant background check system.

Other hurdles include technology. The state of Pennsylvania, for example, cannot figure out how to transfer more than 200,000 state mental health records from its system to the federal database, Rountree said.

Another problem is people lying on applications to purchase guns. In a speech kicking off the two-day conference, New York Mayor Michael Bloomberg outlined a plan for new gun policies that included prosecuting those who lie on firearms purchase applications. Only 44 out of 76,000 such cases were prosecuted in 2010, he said in a speech Monday.

Philip J. Cook of Duke University said one of the greatest limitations of background checks is that criminals do not get their guns from licensed dealers, obtaining them instead from markets that do not require background checks.

One study conducted before the background check rule went into effect found that 80 percent of criminals obtained their guns from a source other than a licensed dealer, he said. Another study suggested that many arrested for murder have no prior felony convictions on their record, he said.

Still, having a record of mental illness archived in the background check system can significantly reduce risk of a violent crime, said Linda Frisman of the University of Connecticut.

But existing laws designed to prevent access to guns through licensed gun dealers will be of limited effectiveness among those with a criminal history and mental health problems, she said.