"This is going to happen again," Texas Attorney General Ken Paxton, a Republican, told Fox News. "All I can say is in Texas at least we have the opportunity to have concealed carry," including in churches, and he suggested "at least arming some of the parishioners so they can respond to something like this."
On the opposite side of the spectrum, Kelley seemed to represent liberal criticisms of the nation's easy access to weapons. He had a record of domestic violence but was allowed to buy four guns between 2014 and 2017, including the high-velocity semiautomatic rifle he used to kill his victims.
Kelley, who served in the Air Force but was kicked out for violent behavior, seems to have fallen between the cracks of the nation's background-check system due to a clerical error.
"It is simply too easy for dangerous people to buy guns, and strengthening our background check system is a critical step in stopping them," Kris Brown, the co-president of the Brady Campaign gun control group, said in a statement.
"All Americans should be asking our leaders, how is it that a man who was court-martialed for domestic abuse and later discharged from the military was able to purchase these guns?" Brown said.
In 2012, Kelley was court-martialed for reportedly cracking his young stepson's skull and assaulting his wife. He was convicted and sentenced to a year of confinement at the Naval Consolidated Brig Miramar near San Diego before receiving a bad conduct discharge in 2014.
"This guy should not have been allowed to buy a gun," said Rachel VanLandingham, a retired judge advocate for the U.S. Air Force who is now a professor at Southwestern Law School, citing federal law.
VanLandingham said that normally when an investigation is opened for a serious offense on an Air Force base, an entry is made into an FBI database.
After the results of a court martial are published, she said, those investigators are supposed to enter the disposition into the database -- which, in this case, would have barred Kelley from buying a gun.
"I don't know where the breakdown happened," she said. "That's the million-dollar question."