The U.S. Air Force failed to report the Texas church gunman’s 2012 domestic violence court-martial to the FBI, which wrongly allowed him to pass background checks to buy guns, officials said Monday.

The revelations came as experts wondered how Devin Patrick Kelley had been allowed to buy four guns between 2014 and 2017 despite spending a year in military prison and getting kicked out of the Air Force for assaulting his wife and reportedly cracking his stepson’s skull.

Investigators have recovered hundreds of shell casings and 15 empty ammo magazines inside the church where Kelley killed 26 people outside San Antonio, investigators said Monday.

The mass shooting at the First Baptist Church in Sutherland Springs may have involved a domestic dispute with relatives who were in the congregation, officials said Monday, discounting religion as a possible motive.

But the gunman’s preparations have made it difficult for investigators to believe he was only targeting a mother-in-law with whom he’d had disagreements, and who attended the church.

“There are many ways that he could have taken care of the mother-in-law without coming with 15 magazines and a loaded assault rifle to a church,” Texas Department of Public Safety Regional Director Freeman Martin said at a news conference.

After publicly identifying Kelley, 26, of Comal County, Texas, as the gunman earlier in the day, by nightfall officials declined to speak his name again, saying “we do not want to glorify him and what he’s done,” Martin said.

Kelley had threatened his mother-in-law — who sometimes attended the church — over text messages before attacking the church on Sunday.

But she was not in attendance as Kelley entered the church during worship services, shooting congregants with a 5.56 mm Ruger semiautomatic rifle while wearing a bullet-resistant vest and a black mask with a white skull on it, officials said.

When Kelley left the building, he was confronted by a neighbor who had armed himself with an AR-15-style rifle.

The two had a gunfight that ended when the neighbor shot Kelley in the leg and the torso, prompting Kelley to drop his rifle and flee in his SUV, with the neighbor and another bystander in pursuit.

As the men chased Kelley out of town, the suspect used his cellphone “to notify his father that he had been shot and that he didn’t think he was going to make it,” Martin said. “Subsequently, he shot himself” in the head. His car drove off the road and crashed. It was unclear whether Kelley shot himself before the crash. Martin said Kelley’s cause of death would be formally determined by a medical examiner.

The mass shooting — the deadliest in the modern history of Texas — has launched national scrutiny over how Kelley was able to buy four guns over the last four years in Colorado and Texas after being convicted of domestic violence in a military court.

Earlier Monday, Texas Gov. Greg Abbott, in an interview with ABC’s “Good Morning America,” referred to Kelley, who served in the Air Force from 2010 to 2014, as “a very deranged individual” who exhibited signs of mental illness long before he was discharged from the military for “bad conduct” after he was court-martialed for assaulting his wife and their child. He was sentenced to 12 months’ confinement.

Though Kelley applied for a legal permit to carry a gun in the state of Texas, he was denied that permit, Abbott said. It was after that he obtained an assault rifle, authorities said.

Investigators found a .22-caliber Ruger and a 9-mm Glock in Kelley’s crashed vehicle.

Investigators still don’t know if Kelley’s military discharge should have barred him from buying guns, said Fred Milanowski, the special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives’ Houston field office.

“In general, if an individual has a dishonorable discharge from the military, they would be prohibited,” said Milanowski, adding that the ATF was still awaiting records from the military.

Sutherland Springs is a rural farming community about 35 miles southeast of San Antonio. As the sun rose Monday, throngs of reporters had descended on the church, which was still cordoned off with yellow police tape. A large tent had been set up outside.

Those killed ranged in age from 18 months to 77 years, authorities said Monday. Among the victims was the preacher’s daughter, 14-year-old Annabelle Pomeroy.

“We were a very close family,” her mother, Sherri Pomeroy — who was out of town with her husband when the attack happened — said of the congregation in a televised news conference Monday.

“We ate together, we laughed together, we cried and we worshipped together,” Pomeroy said. “Now most of our church family is gone. Our building is probably beyond repair … Our sweet Belle would not have been able to deal with losing so much family yesterday.”

The 20 others wounded are 5 to 73 years old, officials said. As of Monday, six were stable or had been released from the hospital, four were in serious condition and 10 were in critical condition.

“Right now, our hearts are going out to all the family members that have lost family, or have family in the hospital,” said Wilson County Sheriff Joe Tackitt.

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