Federal authorities in the USA are taking back guns from thousands of people the background check system should have blocked from buying weapons because they had criminal records, mental health issues or other problems that would disqualify them.

A review found the FBI issued more than 4,000 requests last year for agents from the Bureau of Alcohol Tobacco Firearms and Explosives (ATF) to retrieve guns from prohibited buyers.

It’s the largest number of such retrieval requests in 10 years, according to FBI records – an especially striking statistic after revelations that a breakdown in the background check system allowed a troubled Air Force veteran to buy a rifle later used to kill 26 worshippers at a Texas church last month.

The FBI’s National Instant Criminal Background Check System (Nics) vets millions of gun purchase transactions every year. But the thousands of gun seizure requests highlight persistent problems in a system where analysts must complete background checks within three days of the proposed purchase.

If the background check is not complete within the 72-hour time limit, federal law allows the sale to go forward. ATF agents are asked to take back the guns if the FBI later finds these sales should have been denied.

In addition to the public safety risks, the ATF agents who retrieve the weapons from unauthorised gun owners across the country are exposed to potentially dangerous confrontations.

“These are people who shouldn’t have weapons in the first place, and it just takes one to do something that could have tragic consequences,” said David Chipman, a former ATF official who helped oversee the firearm retrieval programme.

It was not immediately clear how many gun seizure requests agents successfully executed last year or how many weapons were ultimately recovered. Since several firearms can be purchased in a single transaction, the actual number of guns that should have been banned could be even higher.

Mr Chipman, who now advocates for more gun restrictions, called the retrieval process “uniquely dangerous”.

Stephen Morris, a former assistant FBI director, said FBI examiners who review gun purchasers’ backgrounds also recognise the risks.

“They are very aware of the inherent risk to law enforcement officers when they seek a firearm retrieval,” said Mr Morris. “They feel tremendous pressure to make a determination” within the three-day period.

The FBI was overloaded with more than 200,000 background check requests for gun purchases this Black Friday – setting a new single day record. The sudden jump in gun retrieval directives is attributed in part to the record 27.5 million background checks fielded by Nics examiners last year.

Yet the increase is notable in the wake of last month’s decision by Attorney General Jeff Sessions to launch a sweeping review of the vetting system after a reporting breakdown allowed a troubled Air Force veteran to purchase a rifle. Devin Kelley later used the rifle in the November 5 massacre at a Texas church.

Air Force officials have acknowledged that the service failed to transmit a record of Kelley’s court martial for domestic assault to the FBI that would have made him ineligible for the 2016 purchase of the rifle.

The Kelley case highlights longstanding problems with government databases that are rife with incomplete or inadequate record submissions. Mr Morris said that Nics continues to depend on those databases that largely rely on voluntary record submissions from law enforcement agencies, the military and mental health authorities to guard against unauthorised gun purchases.

The government’s success record when it comes to retrieving weapons that were improperly purchased has also been mixed.

The ATF declined to provide information on the 4,170 gun purchases the FBI referred for seizure last year. They reflect a substantial increase from 2,892 requests the previous year.

The FBI said the ATF is not required to report back on the status of the retrieval efforts.

Yet in 2004, the Justice Department’s inspector general found that the ATF’s retrieval efforts were plagued by staffing shortages, technological inefficiencies and a general lack of urgency that resulted in recovery delays of up to a year.

“ATF agents did not consider most of the prohibited persons who had obtained guns to be dangerous and therefore did not consider it a priority to retrieve the firearm promptly,’’ the report concluded.

A separate inspector general’s report last year found marked improvement. Of 125 transactions examined between 2008 and 2014, investigators found that the ATF recovered 116 – or 93 per cent – of the firearms. Of the nine outstanding cases, five buyers could not be found.

Larry Keane, general counsel for the firearm industry trade association National Shooting Sports Foundation, noted that the FBI’s seizure directives represent only a small portion in the flood of of transactions that the bureau has been processing in recent years.

“We support more resources for the Nics operation to process the volume of requests,” Mr Keane said.

This article first appeared in our sister title, USA Today.