COLUMBIA – Federal agents had to track down almost 32,000 people over the last decade who the government eventually determined should not own a firearm but who had been allowed to buy a gun. The purchases occurred because authorities could not complete a background check during a three-day waiting period.

Last year alone, more than 6,000 gun sales were given the green light by the FBI despite background checks that were incomplete and eventually determined the gun owner should not own a firearm, a spokeswoman for the National Instant Criminal Background Check System, or NICS, told The Greenville News.

In those cases, 2,511 guns had to be retrieved by agents of the U.S. Bureau of Alcohol, Tobacco and Firearms, she said.

The waiting-period provision has come under fire recently and critics want the law changed so no gun is transferred until a record check is complete.

Dylann Roof, the 21-year-old charged in the shooting deaths of nine people at an historic black church in Charleston on June 17 and indicted by the federal government this week on hate-crime charges, was allowed to purchase his .45-caliber handgun at a Columbia store because federal authorities could not locate the arrest records within the three-day period that showed a drug charge the FBI says would have disqualified him from purchasing a gun.

Licensed firearm dealers can proceed with a sale if no determination is made by the FBI during the three-day waiting period, though some, such as Wal-Mart, wait until a check is complete before transferring the weapon.

Protest groups this week have asked retailers, including Cabela's, to follow Wal-Mart's lead, and they also have requested Congress to pass legislation to ban the transfer of guns until a background check is complete, no matter how much time it takes.

U.S. Rep. James Clyburn of Columbia, assistant leader of Democrats in the House, has proposed the Background Check Completion Act, which would prevent a gun from being transferred by a licensed dealer until the background check is finished.

"Tragically, the Charleston shooter was allowed to purchase a gun even though the FBI had not completed his background check," Clyburn said. "This should never be acceptable. My bill is a commonsense fix to our nation's gun laws, and I call on my colleagues in Congress to move it immediately towards passage."

Some of his GOP colleagues disagree.

"Law-abiding citizens shouldn't be punished because of the ineptitude of the federal government," said U.S. Rep. Jeff Duncan, a Ware Shoals Republican. "The Administration should focus on making their processes more efficient rather than simply creating more laws and regulations that further erode Americans' 2nd Amendment rights."

U.S. Rep. Trey Gowdy, a Republican representing Greenville and Spartanburg and a former prosecutor, said he voted last year to increase funding for the background check system to ensure states are providing timely and accurate information for the database.

"This is about strengthening NICS to quickly and accurately provide records to ensure only law-abiding citizens can purchase and possess firearms, and it should not take a long time to identify individuals with criminal backgrounds, pending disqualifying charges, or statutorily specific mental instabilities who should not purchase or possess firearms," he said.

"We should ensure law enforcement and the federal government use the NICS system as intended, provide accurate and timely information to the database, and actually prosecute those violators who seek to purchase or possess firearms in violation of currently applicable law before we add additional rules for law-abiding citizens," Gowdy said.

According to the NICS, a branch of the FBI, the agency has asked ATF agents since 2005 to retrieve 31,793 weapons sold to people who should not own a firearm but were allowed to purchase them because a background check could not be completed in three days.

They represent a small fraction of those who the FBI determines should not possess a gun and an even smaller fraction of the number each year who undergo a background check.

Since 1998, the nation has operated under a system in which licensed firearm dealers send the names of those seeking to buy a gun to the NICS, where the agency is able to instantly run a background check in about 91 percent of the cases.

But some cases require further digging and for a variety of reasons, some records cannot be found until after the three-day period. Last year, the number of checks delayed past three days totaled 228,006.

Overall, according to the agency, 90,895 people were denied last year out of 8.2 million transactions.

Of the total denials, more than 38,000 were denied because of a felony conviction or a misdemeanor conviction carrying a sentence of more than two years in prison.

The second-most common reason for denial is the purchaser is a fugitive from justice, according to the agency.

Other reasons for denial include the person being an unlawful drug user or addicted to a controlled substance; having a misdemeanor conviction for domestic violence; someone who has been adjudicated with a mental health issue, an illegal alien or someone who was dishonorably discharged from the military; someone who has been indicted; or who has renounced their United States citizenship.

The NICS agency continues checking a purchaser's background even after the three-day waiting period and up to 90 days, if necessary.

If the denial comes after the three-day period, the dealer is contacted, according to the agency, to see if the gun was transferred.

If it was, then ATF agents must retrieve it.

"The retrieval will be routed to the ATF criminal enforcement group that handles the geographical area where the firearm was obtained," said Gerod King, a spokesman for the ATF's regional office in Charlotte. "Subsequently, the supervisor of that group will assign the retrieval to a special agent. The special agent will contact the prohibited person and retrieve the firearm. The United States Attorney's Office in that district makes the decision to prosecute or not prosecute the prohibited purchaser."

Thus far, the system has denied 1.1 million gun purchases as a result of background checks.

More than 200 million background checks have been processed since 1998, according to the NICS.