The ex-wife of Devin Kelley, the man responsible for the massacre at a Texas church last Sunday, said her former husband had a "lot of demons inside of him" and had previously threatened to kill her entire family.

"He just had a lot of demons or hatred inside of him," Tessa Brennaman, 25, told "Inside Edition of Kelley, who killed 25 people, including children, at the First Baptist Church in Sutherland Springs earlier this month.

She recalled how one day, he threatened her after she got a speeding ticket: "He had a gun in his holster right here and he took that gun out and he put it to my temple and he told me, 'Do you want to die? Do you want to die?'"

The couple finally divorced in 2012, and in 2013, Kelley pled guilty to choking Brennaman, pulling her hair and kicking her. He also pleaded guilty to hitting her young son's head and body, fracturing his skull, and was subsequently sentenced to a year in a military prison. He was later removed from the military with a bad-conduct discharge and a reduction of rank.

Last week, the US Air Force admitted it had failed to notify federal authorities of the conviction, which would have meant Kelley was banned from purchasing the Ruger AR-556 rifle and two handguns he used in the shooting.

Jessika Edwards, a former Air Force staff sergeant who said she worked with Kelley at Holloman Air Force Base in New Mexico, told CNN that Kelley often got into trouble.

"It was problem after problem," she said. "He would make jokes about wanting to kill somebody," she said.

The shooting, which left dozens dead 20 others injured, stemmed from a domestic dispute involving Kelly and his mother-in-law, who was a member of the church community but was not present on the day of tragic event.

Shortly before the shooting, Kelley attended a Halloween event at the church acting strangely and dressed all in black, alerting some members.

One member of the community, Judy Green, said he was "completely distant and way out in thought".

"He didn't even blink - he just stared," she said. "There was something wrong with the picture. I was thinking forward, and that was what was scaring me."

Several evangelical leaders have condemned the shooting as "satanic," including "Focus on the Family" founder Dr. James Dobson.

"Shirley and I are heartbroken by today's horrific church shooting," he said. "Words cannot express the sorrow we feel for the residents of this small Texas community that has been ripped apart by a truly heinous and senseless act. Tragically, as one pastor said when interviewed, this was a demonic act of wanton murder. Indeed it was."