After that breach, Congress struck a delicate bargain with the National Rifle Association and passed legislation offering states grants to add more mental health records to the instant-check system.
A domestic violence update could be next, especially for violators in or discharged from the military. An online repository of active records maintained by the F.B.I.’s Criminal Justice Information Services shows that the Department of Defense had reported just one case of domestic violence as of Dec. 31, 2016. Although federal law lists 11 criteria that would bar someone from purchasing a gun — including being the subject of a protective order for domestic violence or conviction of a domestic violence misdemeanor — all but a tiny handful of the military’s 11,000 reported cases were in one category: dishonorable discharge.
Mr. Blumenthal, long a proponent of expanding gun safety laws, said that if the records in the online repository are accurate, it would be a “major lapse.”
A 2015 Inspector General review faulted the Defense Department’s level of compliance with the Lautenberg Amendment, as the 1996 law is known, but focused on vetting current and future service members, not on how military domestic violence cases were reported to the federal database. Laura Cutilletta, the legal director of the Giffords Law Center to Prevent Gun Violence, said her group had reviewed multiple military documents pertaining to compliance with the Lautenberg Amendment and had not found a procedure for reporting convictions to the F.B.I.
“Clearly, they do have a process,” she said, but “they’re only sending the dishonorable discharges.”
Experts who investigate mass shootings say a history of domestic violence is often a missed clue. One example: the June 2016 shooting at the Pulse nightclub in Orlando, Fla. The wife of Omar Mateen, the gunman, described him in an interview with The New York Times as someone who angered easily, beat her and lived his life in secret.
Credit Todd Heisler/The New York Times
“We have seen over and over this pattern where in these notorious mass shootings, it is a very common thread where the person had a particular history of domestic violence,” said Billy Rosen, the deputy legal director for Everytown for Gun Safety. “A history of this particular kind of conduct may really demonstrate that someone has dangerous propensities and should not be allowed to have guns.”
Using F.B.I. data and other publicly available information, Everytown analyzed mass shootings in the United States that occurred from 2009 to 2016, defining a mass shooting as one in which four or more people were shot and killed, not including the shooter. Of 156 shootings that fit that category, 54 percent were “related to domestic or family violence,” the analysis found.
In the case of Mr. Kelley, he entered a pretrial agreement — much like a plea bargain in the civilian world — where he pleaded guilty in return for capping his maximum sentence at 18 months. He was sentenced to a year of confinement, a reduction in rank from airman first class to airman basic and was discharged for bad conduct, according to Don Christensen, a retired colonel who was the chief prosecutor for the Air Force at the time.
Mr. Christensen said he believed that the assault case disqualified Mr. Kelley on two separate grounds under federal law from owning a gun.
The first was pleading guilty to a crime with a maximum punishment of more than a year’s confinement; the assault on the stepson would have had a maximum of five years. The second, he said, was the Lautenberg Amendment.
“The real story is why, with these offenses, was he still able to buy a gun?” Mr. Christensen said. “He clearly should not have been able to.”
He noted that the military justice system uses different terminology than civilian criminal courts, which could explain why Mr. Kelley’s conviction was not reported. “That could be part of the problem here, our use of archaic terms that don’t translate well to the civilian world,” he said.
When Congress adopted the Lautenberg Amendment in 1996, the nation was in the mood to enact gun safety laws, said Richard Aborn, a longtime advocate for gun safety and the former president of the Brady Center, which advocates gun control. Lawmakers had already adopted a ban on military-style assault weapons — that law has since lapsed — and prohibited the purchase of large-capacity ammunition magazines.
But the Gun Control Act of 1968, which regulated the purchase of firearms, stipulated that only convicted felons could be prohibited from buying guns. “The question kept coming up, what about domestic violence, because its often a misdemeanor, and we knew that there was a linkage between gun violence and domestic violence,” Mr. Aborn said. “That was the birth of the whole conversation.”
But the law’s definition of who is a domestic abuser is “quite specific,” said Mr. Rosen, of the Everytown group. The measure requires, for example, that the victim and the abuser have to have been married or have had a child together, or have lived together. Thus the Lautenberg Amendment does not apply to people who are dating, which gives rise to what advocates call “the boyfriend loophole.”
Senator Amy Klobuchar, Democrat of Minnesota, has introduced legislation that would close that loophole, and would also prevent stalkers from having guns. A 2014 report by the liberal-leaning Center for American Progress reviewed conviction records in 20 states, and found that nearly 12,000 people across the country had been convicted of misdemeanor-level stalking, but were still permitted to own guns.
“The Lautenberg Amendment was bare bones,” said Kim Gandy, the chief executive of the National Network to End Domestic Violence. “There are a lot of gaps in the instant criminal justice system; the data is only as good as what goes into it. So if the data is not in the system, obviously there is a giant loophole there.”