More than 4,000 guns had to be retrieved from buyers after delayed background checks last year

— -- More than 4,000 guns that were transferred into the hands of buyers in 2016 were later referred to the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) for retrieval because the purchasers were found to be prohibited from buying a gun.

Background checks for firearms purchases have been under the spotlight since it was discovered that the suspect in a deadly rampage last month at a Texas church was able to purchase an assault rifle despite a law that restricts people convicted of domestic violence from buying such weapons.

When a gun purchase is made by a federally licensed gun dealer, the Federal Bureau of Investigation (FBI) is required to run a background check. By federal law, this must be completed in three days, or the sale in some states is approved by default.

However, the work to determine if the purchaser is prohibited from possessing a firearm can continue after the sale and in some cases, a determination is made that the buyer should be prohibited from having a gun after it is already sold.

When this kind of “delayed denial” occurs, the case is referred to ATF for retrieval.

Once that happens, either state authorities or ATF go knocking on doors to get the gun back.

In 2016, that happened 4,170 times, as first reported by USA Today

The FBI processed more than 51 million NICS transactions from 2008 to 2014, of which 556,496, or about 1 percent, were denied, according to the Department of Justice (DOJ) Office of the Inspector General (OIG).

Background checks have been on the rise. Black Friday 2017 was the new single-day record for gun checks at more than 200,000, according to the FBI.

When asked about the current success rate of ATF recoveries, a spokesperson said that the information was not publicly available.

A September 2016 DOJ Inspector General report found that “ATF generally has an appropriate system of controls for processing NICS denials that are referred by the FBI.”

ATF recovered 93 percent of the sample of 125 firearms that required recovery, according to the report.

Gun laws across the states are inconsistent. Some states, like California, have a 30-day waiting period for purchases, so delayed denials are generally not a problem there.

On Nov. 22, following the revelations that the criminal history of the Texas church shooter Devin Kelley was not properly entered into the correct database, Attorney General Jeff Sessions directed the FBI and ATF to conduct a comprehensive review of the background check system.

Kelley, 26, killed 26 people and injured at least 20 others on Nov. 5, 2017, at the First Baptist Church of Sutherland Springs, Texas. He died of a self-inflicted gunshot wound after the shooting.

“The recent shooting in Sutherland Springs, Texas revealed that relevant information may not be getting reported to the NICS -- this is alarming and it is unacceptable,” Sessions said in a statement at the time.