The Obama administration ordered the removal of over 500,000 fugitives with outstanding arrest warrants from the National Instant Criminal Background Check System (NICS) in late 2016, according to testimony from Acting FBI Deputy Director David Bowdich.

Bowdich confirmed a November report from the Washington Post which set the figure at "tens of thousands," after Sen. Dianne Feinstein (D-CA) asked him if more than 500,000 names were dropped from the database. 

The FBI purged the names from the database after the Justice Department 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. -WaPo

“That was a decision that was made under the previous administration,” Bowdich testified.

“It was the Department of Justice’s Office of Legal Counsel that reviewed the law and believed that it needed to be interpreted so that if someone was a fugitive in a state, there had to be indications that they had crossed state lines,” said Bowdich. “Otherwise they were not known to be a fugitive under the law in the way it was interpreted.”

Since its creation in 1998, the NICS system has prevented 1.5 million people from purchasing a firearm, including 180,000 denials to fugitives from justice, according to government statistics. 

While the FBI had a broad definition of "fugitive," meaning anyone with an outstanding arrest warrant, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) definition narrowed the definition to anyone with a warrant who has crossed state lines. The DOJ Inspector General, Michael Horowitz, urged the Justice Department to address the disagreement in terms "as soon as possible." 

Shortly before President Trump took office, the DOJ Office of Legal Counsel went with the ATF definition.

“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. -WaPo

“The Justice Department is committed to working with law enforcement partners across the country to help ensure that all those who can legally be determined to be prohibited from receiving or possessing a firearm be included in federal criminal databases,” a Justice Department official told the Washington Post last November.