The Air Force says it failed to follow policies for alerting federal law enforcement about Devin P. Kelley’s violent past, enabling the former service member, who killed at least 26 churchgoers Sunday in Sutherland Springs, Tex., to obtain firearms before the shooting rampage.

Kelley should have been barred from purchasing firearms and body armor because of his domestic violence conviction in 2014 while serving at Holloman Air Force Base in New Mexico. He was sentenced to a year in prison and kicked out of the military with a bad conduct discharge following two counts of domestic abuse against his wife and a child, according to Air Force spokeswoman Ann Stefanek.

“Initial information indicates that Kelley’s domestic violence offense was not entered into the National Criminal Information Center database,” Stefanek said in a statement released Monday. Air Force Secretary Heather Wilson and Chief of Staff David Goldfein have directed an investigation of Kelley’s case and “relevant policies and procedures,” she said.

Firearms retailer Academy Sports also confirmed Monday that Kelley purchased two weapons from its stores after passing federal background checks this year and last. It remains unclear whether those were the same weapons used in Sunday’s massacre, but his ability to buy guns at all highlights the Air Force’s failure to follow Pentagon guidelines for ensuring that certain violent offenses are reported to the FBI.

Although military law does not classify crimes as felonies or misdemeanors, Kelley’s sentence was a functional felony conviction, said Geoffrey Corn, a former Army lawyer and professor at the South Texas College of Law in Houston. A separate law prohibits violent offenders from purchasing body armor, which Kelley was seen wearing during the rampage.

[Death sweeps across 3 generations of a single family gathered at Texas church]

Authorities say Kelley, dressed in all black and wearing a tactical vest, entered the Sutherland Springs First Baptist Church and opened fire with a Ruger semiautomatic rifle. The AR-556 he used is patterned on the ubiquitous AR-15.

An FBI Evidence Response Team sweeps the lot next to the First Baptist Church in Sutherland Springs, Tex., on Nov. 6, after a shooting there. (Carolyn Van Houten/The Washington Post)

As news emerged Monday that the Air Force failed to follow notification policies in Kelley’s case, lawmakers called on Defense Secretary Jim Mattis to determine how many former service members who’ve been convicted of violent crimes also have been improperly documented.

“Learning that this senseless act of violence might have been prevented if only the proper form was filled out by military investigators was absolutely devastating,” Sen. Kirsten Gillibrand (D-N.Y.) said in a statement. Sen. Richard Blumenthal (D-Conn.) said on Twitter that he would call on the Pentagon and the Justice Department to “provide a clear picture of where, why and how this process failed.”

Mattis said Tuesday that he has directed the Pentagon’s inspector general to investigate further.

“If the problem is that we didn’t put something out, we’ll correct that,” he said. “There is at least an indication in what I’ve read in the press and what I’m getting through other elements of the government — not the Department of Defense — that the direction is out there. I’ve got to make sure. I don’t want to make assumptions right now.”

Corn said it appears that there is confusion within the Air Force, and other military branches, about reporting only violent crimes that result in dishonorable discharges, which are more severe punishments under military law than the bad conduct discharge Kelley received.

[Read Kelley’s court documents]

“Either the Department of Defense is reporting these convictions, or they’re not,” Corn said. “How is the federal statute going to be effectively implemented if they aren’t reporting these convictions?”

Texas state officials had said previously that Kelley did not meet the requirements for obtaining a concealed handgun license, according to a report in the Houston Chronicle. Kelley also claimed he had no criminal background that would have precluded him from buying firearms, the newspaper reported.

In the initial aftermath of Sunday’s massacre, officials were searching for answers about how Kelley obtained his weapons.

“By all of the facts that we seem to know, he was not supposed to have access to a gun, so how did this happen?” Texas Gov. Greg Abbott (R) said in an interview Monday morning on CNN.

[Texas officials say before massacre, gunman had threatened his mother-in-law, who attended the church]

Sky Gerrond, a former Air Force security operations officer who spent seven years in military law enforcement, said a dishonorable discharge may have been a more appropriate punishment for the severity of Kelley’s crime. Had the Air Force court system handed down that punishment, Gerrond said, it is more probable that the details of Kelley’s conviction would have reached the FBI’s database.

The Air Force does not operate prisons and instead sends troops convicted of crimes to Army or Navy jails. Kelley served his sentence at a Navy brig in San Diego. Navy regulations do not require a fingerprint card and conviction summary to be forwarded to the FBI after inmate in-processing.

Corn said inmates are briefed on the specific restrictions they face upon returning to society. Gun ownership, he said, would be at the top of the list for Kelley.

“What do we tell guys like him when they leave?” Corn said.

Dan Lamothe contributed to this report.