Experts have been warning since the Department of Justice changed its gun background check policy earlier this year that dangerous criminals would have a better chance of purchasing guns legally.

A case out of Arizona, they say, validates their concerns.

In early November, just days after police issued a warrant for his arrest in the murder of a 15-year-old boy, Tristan Beardsley walked into a Walmart in Tucson and tried to buy a gun.

“Here’s a known gang member who is wanted for murder,” said Anthony Coulson, who heads Arizona’s National Instant Criminal Background Check System Task Force and described the event to The Trace. “He was probably not acquiring a firearm for legitimate purposes.”

Before the rule change, Beardsley’s attempted purchase would have been quickly rejected. The store clerk would have called the Federal Bureau of Investigation’s background check center, setting in motion a process that would have led to a denial on the grounds that he had an open arrest warrant.

Tristan Beardsley.

But in February, the DOJ began requiring that background check screeners only deny gun purchases to some people with open arrest warrants — those who had fled across state lines in order to escape justice.

By that definition, Beardsley would not have been prohibited. He was standing less than five miles from the murder scene and had not crossed state lines.

In the end, Beardsley was not able to buy the gun. But experts say it wasn’t his murder warrant that prevented him from doing so.

Beardsley’s lawyer, Craig Kessler, said he didn’t know anything about his client’s attempt to buy a gun and could not comment for this story. Beardsley has pleaded not guilty to the murder.

A spokesman for the FBI declined to comment on exactly what happened when Beardsley tried to buy the gun, saying the agency does not reveal information about individual NICS checks. But Coulson, who was briefed on the case because of his position on the NICS Task Force, explained how events unfolded.

Because Beardsley’s open arrest warrant didn’t automatically prohibit him from buying a gun, background checkers needed to do more research. This meant calling local authorities for details about his warrant.

That process took more than three days. Some contact numbers for law enforcement and the courts proved to be outdated — a common problem across the country, Coulson said.

According to federal law, licensed gun dealers can release a gun to a prospective buyer if the background check isn’t finished within 72 hours. Many gun dealers follow that guideline, and release the gun after the period ends. Such sales, known as “default proceeds,” last year resulted in at least 4,000 guns falling into the hands of people who shouldn’t have had them, according to a recent USA Today report.

But Walmart has an uncommonly strict policy requiring clerks to get a clear approval or denial from background checkers before releasing a gun to a buyer.

A spokesperson for Walmart did not respond to a request for comment.

Laura Cutilletta, the legal director of the Giffords Law Center to Prevent Gun Violence, said Beardsley offers a sharp example of why the new definition poses a danger to the public.

Somebody who’s wanted for a crime is not someone who should have a gun,” she said, “Not only have they broken the law, but they have evaded the law.”

U.S. Marshals picked up Beardsley for murder on Nov. 14,  just as the three-day waiting period was running out, sources close to the case said. He did not have a gun, according to a Marshals spokesman.