Twenty years ago, a pair of students killed a teacher and a dozen of their classmates at a high school in Littleton, Colo. The shooters at Columbine High School used semi-automatic weapons and sawed-off shotguns in the attack before turning the guns on themselves.
Just a few months before that shooting, the FBI launched the National Instant Criminal Background Check System to try to prevent dangerous individuals from purchasing guns.
And in the two decades since, the federal government says it has conducted hundreds of millions of background checks. With critical shortcomings in the system, though, mass shootings continue in the U.S.
"The weakness of the NICS system is talked about mostly in the wake of a tragic shooting, which happens more often than not," says Stephen Morris, a former FBI assistant director for the Criminal Justice Information Services Division, which oversees NICS.
NICS functions today much like it did 20 years ago. When someone wants to buy a firearm, a federally licensed gun dealer contacts the system. Usually within minutes, federal investigators receive the request and begin searching for clues within three main databases to approve or deny the purchase.
The FBI says the system has denied more than 1.3 million firearm transfers since NICS first began operating.
If more research needs to be done, the purchase can be delayed for up to three business days. If in that time investigators can't complete the additional background check, federal law allows the gun dealer to proceed with the transaction.
In 2015, a white supremacist in Charleston, S.C., was able to obtain a gun after the FBI failed to complete his background check before the three-day deadline.
The gun purchase was able to go through and that shooter later killed nine black churchgoers.
As NPR reported later, it was discovered the shooter had admitted possessing a controlled substance during an arrest. That should have been sufficient to deny the purchase on the grounds of "an unlawful drug user or addict."
Since it was created in late 1998, NICS has initiated some 311 million background checks, including 26 million in 2018 alone, the federal government says.
"We're talking about a system and a process that was created over 20 years ago. It goes without saying the system is stressed out," says Morris, the former FBI official.
The NICS system relies on state and local agencies to make the data more robust, but sometimes records can be missing or incomplete.
"Like any database, the system is only as good as the records put in that system," says Lawrence Keane of the National Shooting Sports Foundation. "There are some very real world examples of where the background check system was not accurate."
Consider the Virginia Tech shooting in 2007, in which 33 people died, including the gunman.
In that case, Virginia court documents released after the rampage showed a judge had previously declared the man "mentally ill" and ordered him to seek treatment. But at the time, Virginia wasn't fully sharing information with NICS. Had that information been in the system, there is a better chance the gunman would not have been able to obtain his guns.
In 2017, a gunman killed 27 people including himself in Sutherland Springs, Texas. He was an Air Force veteran and purchased an assault-style rifle and two handguns, but a domestic violence conviction during his time of service should have barred him from possessing the weapons. The Air Force never entered that information into NICS.
Following those attacks, Congress passed legislation to try to address the lapses, including offering states more financial incentives to share information with NICS.
After high-profile shootings, gun violence prevention advocates often renew their calls for universal background checks. Those would require background checks on virtually all gun sales, not just ones administered by federally licensed gun dealers.
Keane, with the gun industry trade association, says he doesn't think federal universal background checks are the solution.
"We think we have to work to fix the NICS system before you even have a conversation about expanding it," Keane says. "That does not make sense to us to expand background checks, through so-called universal background checks, when the system we have now is not working as it should be."
But 20 states, including California, Connecticut and Vermont, extend background checks to include private sales of at least some firearm transactions. That's according to Giffords Law Center to Prevent Gun Violence.
Just this week, an 18-year-old woman, who authorities say had an "infatuation" with the Columbine High School shooting, flew from Miami to Denver and within hours purchased a shotgun along with ammunition.
More than a dozen school districts in the Denver area, including Columbine High School, were closed Wednesday while a "massive manhunt" was underway for the woman. Her body was recovered later that day, after she apparently killed herself.
The gun shop owner who sold the guns posted on Facebook that the woman passed both the Colorado Bureau Investigation background check system as well as NICS.
"She did go through the full background check, and was given a clearance by both NICS and CBI," wrote Josh Rayburn. "We had no reason to suspect she was a threat to either herself or anyone else."
A previous Web version of this story incorrectly said the mass shooting at Virginia Tech was in 2017. It took place in 2007.
SACHA PFEIFFER, HOST:
Twenty years ago today, President Clinton addressed the nation after 13 people were killed by a gunman at Columbine High School in Colorado.
(SOUNDBITE OF SPEECH)
BILL CLINTON: Hillary and I are profoundly shocked and saddened by the tragedy today in Littleton, where two students opened fire on their classmates before apparently turning their guns on themselves.
PFEIFFER: Just months before that shooting, the federal government had established a background check system for gun purchases, and the FBI says it has conducted more than 300 million background checks since then. But mass shootings continue to plague the country. NPR's Brakkton Booker reports on some of the shortcomings of the system.
BRAKKTON BOOKER, BYLINE: Back in 1999, President Clinton called the National Instant Background Check System, or NICS for short, a powerful crime-fighting tool.
(SOUNDBITE OF SPEECH)
CLINTON: Since our new instant criminal background check system went into effect, 100,000 illegal purchases have been stopped by the insta-check system.
BOOKER: It is designed to work quickly, and 20 years later, it still does. A federally licensed gun dealer contacts NICS when someone tries to buy a gun. The dealer is told the purchase is approved or denied. There's also one other possibility - the transaction can be delayed for up to three business days.
LAWRENCE KEANE: If after three business days, and they have not gotten a response one way or the other from NICS, they are permitted by law to transfer the firearm.
BOOKER: That's Lawrence Keane of the National Shooting Sports Foundation. He says the gun transaction can go through even if the FBI hasn't completed the background check in the allotted time frame.
KEANE: Like any database, the system is only as good as the records that are put into the system.
BOOKER: The system relies on a collection of state and federal records, but it's sometimes incomplete. That became clear nearly eight years to the day after the Columbine shooting.
(SOUNDBITE OF SPEECH)
GEORGE W BUSH: Our nation is shocked and saddened by the news of the shootings at Virginia Tech today.
BOOKER: That shooter would have been denied his gun purchases, but important court documents declaring him a danger to himself never made it into the NICS system. And this wasn't the last time the system failed. In 2017, the shooter in Sutherland Springs, Texas, should not have been able to obtain a weapon. He went on to kill 27 people, including himself. A few years before that, there was another system failure in Charleston, S.C.
(SOUNDBITE OF SPEECH)
BARACK OBAMA: I've had to make statements like this too many times. Communities like this have had to endure tragedies like this too many times. We don't have all the facts, but we do know that once again, innocent people were killed, in part because someone who wanted to inflict harm had no trouble getting their hands on a gun.
BOOKER: In that shooting, nine black churchgoers were killed by a white supremacist. It was Stephen Morris who oversaw the FBI background check division at the time of the Charleston shooting.
STEPHEN MORRIS: Generally, the weaknesses of the NICS system are talked about mostly in the wake of a tragic shooting, which seems to be more often than not.
BOOKER: In the Charleston case, the FBI delayed the gun transaction. But because of poor communications between federal and state authorities, the background check wasn't resolved in three business days. So the gun purchase went through in what's called a default proceed. It was later discovered the shooter previously admitted to possessing a controlled substance, and that would have triggered a deny for the handgun.
Over the years, the FBI says it's denied some 1.3 million gun transfers. But Morris says, even with tweaks to the system, lawmakers haven't done enough to ease the strain on federal investigators.
MORRIS: The one area that legislators - Congress, specifically - could release some of that pressure is extending that deadline.
BOOKER: It's not just the crunch to conduct a search in three business days. It's also the sheer volume of checks. The FBI says it's conducted more than 300 million background checks, including 26 million just last year. Again, Stephen Morris.
MORRIS: We're talking about a system and a process that was created over 20 years ago. It goes without saying that the system is stressed out.
BOOKER: In addition to the system being stressed out, Morris says it's also limited, unable to catch thousands of other firearms transactions, legal and illegal, that wouldn't trigger the NICS system, like in Parkland, Fla.
(SOUNDBITE OF SPEECH)
PRESIDENT DONALD TRUMP: A school filled with innocent children and caring teachers became the scene of terrible violence, hatred and evil.
BOOKER: Intent - it's one more thing NICS can't detect. So once a gun is purchased, the background check system no longer provides a safeguard.
Brakkton Booker, NPR News.
(SOUNDBITE OF PAUL WHITE'S "RETURNING") Transcript provided by NPR, Copyright NPR.