The Texas massacre that unfolded on Sunday was perpetrated by a man who should not have been allowed to buy any guns, but a clerical error led to his being easily armed.

Why did he lose his right to buy guns?

Patrick Devin Kelley had a long list of violent incidents in his life, but one in particular should have prevented him from buying guns. In 2012 Kelley was convicted for domestic assault against his then-wife and her son.

Under U.S. law, his right to buy guns should have been taken away after that.

Why was he allowed to buy guns?

Kelley was armed with a rifle and two handguns that he himself had purchased when he attacked churchgoers at the Sutherland Springs Baptist Church.

Although Kelley should have been banned from buying guns, NPR's Tom Bowman reported that the U.S. Air Force neglected to report the conviction on a national database.

NPR's @TBowmanNPR reports Kelley was able to purchase firearms because @usairforce failed to enter assault conviction in federal database.

— NPR (@NPR) November 6, 2017

At the time of the domestic assault, Kelley was a member of the Air Force, and he plead guilty in his court martial to assaulting his wife and "intentionally inflicting grievous bodily harm" to her child.

What did the Air Force say about this?

"This was mishandled by the Air Force Office of Special Investigations at Holloman Air Force Base in New Mexico, where Kelley was serving when he was arrested," Bowman reported.

"An investigation is now underway, and the Air Force is taking it very seriously, said the source."