This is an archived article that was published on sltrib.com in 2016, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

Omar Mateen, who killed 49 people in an Orlando nightclub Sunday, was a walking red flag. He was abusive, unstable and prone to rages. He boasted of ties to every terrorist group under the sun. He expressed a vast catalog of hatreds and resentments. According to a former colleague, he "talked about killing people all the time."

These warning signs didn't go unnoticed. The FBI added Mateen to its main terrorist watch list, placed him under surveillance, prodded him with an informant, recorded his conversations and interrogated him more than once.

And yet, earlier this month, Mateen walked into a gun shop, passed a background check, and lawfully purchased a rifle, a handgun and enough ammunition to sustain an insurgency. The result was no less awful for being predictable.

Stopping such purchases should be a priority. The FBI is already alerted, through the National Instant Criminal Background Check System, when someone on its terrorist watch list tries to buy a gun through a federally licensed dealer. Since 2004, according to the Government Accountability Office, people on the watch list have tried to buy or obtain permits for firearms 2,474 times. Yet fully 91 percent of those transactions were allowed to proceed.

That's nuts. And as terrorists increasingly turn to firearms for their attacks, it's asking for another tragedy.

Some in Congress have been trying to close this odd loophole for almost a decade. One sensible bill, now being revived, would allow the attorney general to intervene if someone reasonably suspected of engaging in terrorism tries to buy a gun. It also offers a legal avenue to appeal such decisions.

That's a promising approach. Giving the attorney general discretion makes more sense than requiring strict adherence to a given watch list. (Mateen, pertinently, had been removed from the list when the FBI closed an investigation on him.) And while killers will still have other ways to get firearms — on the internet, at gun shows — that's a poor excuse for inaction.

Owning a gun is a right in America. But freedoms, even those protected by the Constitution, can be reasonably limited for reasons of public safety. The First Amendment doesn't protect fraud; the Second doesn't extend to felons or the mentally ill. Excluding suspected terrorists from arming themselves is no less sensible. It might even prevent the next Omar Mateen, the next calamity, the next round of anguish and grief.