RICHMOND, Va. (AP) — Dozens of relatives of people killed or wounded in the 2007 Virginia Tech shootings sent a letter to the presidential candidates Thursday asking how they would improve a background check system designed to prevent dangerous people from buying guns.

In their letter to President Barack Obama and Republican challenger Mitt Romney, the 67 family members said that five years after the Tech shootings, millions of mental health records are still missing from a national database of prohibited gun purchasers.

"Now is the time to fix our nation's broken gun laws, but we need our nation's leaders to tell us the specific steps you will take to prevent more bloodshed," they wrote.

The Romney campaign did not immediately respond to an email request for comment.

The White House did not respond directly to the letter-writers' demand but pointed to a speech last month in which Obama told the National Urban League that "a mentally unbalanced individual should not be able to get his hands on a gun so easily."

Seung-Hui Cho, the Virginia Tech student who killed 32 people before killing himself, was able to buy two guns even though he had been ruled a danger to himself during a court hearing in 2005 and was ordered to undergo outpatient mental health treatment. Federal officials said that Cho should have been barred from buying weapons but that the records were never forwarded to the background-check system. Virginia officials, however, said state law required the names of only those committed to mental hospitals. The loophole has since been closed by state law, and people in Virginia who undergo outpatient treatment are now entered into the database

Lori Haas, whose daughter Emily was wounded in the Virginia Tech shootings, said the database now has the names of more than 140,000 Virginians. In contrast, more than 20 states have less than 100 names in the database.

"The fact of the matter is, we still have a broken system where dangerously mentally ill people can get their hands on firearms," Haas said.

She said officials in some states mistakenly believe the federal privacy laws governing mental health records prevent them from submitting names to the database. She said those laws apply to mental health providers, not courts that determine a person is too mentally unstable to buy a gun.

The mailing of the letter coincides with the Mayors Against Illegal Guns coalition's release of an interactive map showing how many mental health records states have reported. The map, available at http://www.demandaplan.org/fatalgaps , is based on the most recent FBI data, also lists the number of gun background checks conducted in each state in 2011.