WASHINGTON — Tens of thousands of people wanted by law enforcement officials have been removed this year from the FBI criminal background check database that prohibits fugitives from justice from buying guns.

The names were taken out after the FBI in February changed its legal interpretation of “fugitive from justice” to say it pertains only to wanted people who have crossed state lines.

What that means is that those fugitives who were previously prohibited under federal law from purchasing firearms can now buy them, unless barred for other reasons.

Since the National Instant Criminal Background Check System was created in 1998, the background check system has prevented 1.5 million people from buying guns, including 180,000 denials to people who were fugitives from justice, according to government statistics. It is unclear how many people may have bought guns since February who previously would have been prohibited from doing so.

Attorney General Jeff Sessions sent a memo Wednesday to the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives instructing them to take several steps to improve NICS.

The system, he said, is “critical for us to be able to keep guns out of the hands of those . . . prohibited from owning them.”

The criminal background check system has come under scrutiny in recent weeks after the Air Force said it failed to follow policies for alerting the FBI about the domestic violence conviction of Devin Kelley, who killed more than two dozen churchgoers in Sutherland Springs, Texas, this month. Because his conviction was not entered into NICS, Kelley was allowed to buy firearms.

Two years ago, Dylann Roof, who killed nine people at a historic black church in Charleston, South Carolina, was able to buy his gun after errors by the FBI and local law enforcement led to his name not being entered into criminal record databases when he was arrested and had admitted to drug possession.

The interpretation of who is a “fugitive from justice,” a category that disqualifies people from buying a gun, has long been a matter of debate in law enforcement circles – a dispute that ultimately led to the February purging of the database.

“Any one of these potentially dangerous fugitives can currently walk into a licensed gun dealer, pass a criminal background check, and walk out with a gun,” Robyn Thomas, executive director of the Giffords Law Center to Prevent Gun Violence, wrote in a letter to FBI Director Christopher A. Wray on Wednesday. The Giffords organization, founded by former Arizona congresswoman Gabrielle Giffords, called on the FBI and ATF to “correct this self-inflicted loophole” and recover all guns illegally purchased this year because of the purge of names from the database.

For more than 15 years, the FBI and ATF disagreed about who exactly was a fugitive from justice. The FBI, which runs the criminal background check database, had a broad definition and said that anyone with an outstanding arrest warrant was prohibited from buying a gun. But ATF argued that, under the law, a person is considered a fugitive from justice only if they have an outstanding warrant and have also traveled to another state.