&/or a dishonorable discharge and were on the Do not buy list (though it would be illegal for the buyer):
http://www.nydailynews.com/news/national/texas-shooter-bad-conduct-discharge-allowed-buy-guns-article-1.3614862
... He did not have a license to carry a weapon, but he did have a valid private security license.
“There were no disqualifiers entered into the database that would preclude him from getting the license,” said Freeman Martin of the Texas Department of Public Safety. “The databases were checked, and he was cleared.”
But Kelley did not have to go to a licensed dealer to buy a gun. In Texas, it’s legal to do a “private purchase,” meaning buy a gun from a private citizen.
Sales like these happen at gun shows, but they can also happen between neighbors or via online websites like Texasguntrader.com — with no background check.
“Getting a gun in this country is remarkably easy to do,” one Texas gun dealer said.
“If you own a firearm, you could go knocking on people's doors and say ‘Do you want to buy this firearm for $100?’ and if they say ‘Yes,’ you could hand them the gun and take the cash and that is a legal transaction. There is no background check.”
Edited by JeffB at 18:17:25 on 11/06/17