Alamogordo, New Mexico (CNN) Texas church shooter Devin Kelley claimed he bought animals on Craigslist with the sole intention of killing them, a former Air Force colleague told CNN.

Jessika Edwards, who says she worked with Kelley at Holloman Air Force Base in New Mexico from 2010 to 2012, said Kelley told her he was "using the dogs as target practice."

The morbid admission came in Facebook messages starting in 2014, Edwards said, after the two reconnected in civilian life. Though Edwards can't say whether Kelley was telling the truth, the odd behavior was enough for her to stop communicating with him.

Edwards said Kelley also displayed a fascination with mass murders while he was enlisted in the Air Force.

"He would make jokes about wanting to kill somebody," Edwards recalled. "And we would say, 'wait, that's not funny.'"

The obsession was so pronounced, Edwards said, that when Kelley was disciplined for poor performance she told her bosses to "back off or he would shoot the place up."

A law enforcement source close to the Texas shooting investigation confirmed to CNN that FBI agents interviewed Edwards about her interactions with the gunman.

'Problem after problem'

"He was always getting into trouble," Edwards said of Kelley. "It was problem after problem."

In 2012, Kelley was court-martialed and convicted for assaulting his wife and stepson. Edwards said those domestic problems boiled over on the job and Kelley would come in depressed and unfocused.

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"He threatened to kill himself one time if I didn't let him go see a chaplain," Edwards said. As a staff sergeant, Edwards says she supervised Kelley.

The US Air Force confirmed to CNN that Edwards was at Holloman Air Force Base at the same time as Kelley, but did not confirm whether she worked with him.

Edwards said that "everything that could be done was done" for Kelley. In addition to regular sessions with a chaplain, she says Air Force officials referred him to the mental health office.

In the days since Kelley's shooting massacre, the Air Force has been criticized for failing to notify federal law enforcement officials of Kelley's conviction. Had federal authorities been aware, Kelley should have been barred from legally purchasing the weapon he used in the Sutherland Springs, Texas, attack

Photos: Sutherland Springs church shooting Investigators work at the scene of a mass shooting at the First Baptist Church in Sutherland Springs, Texas, on Sunday, November 5. A man opened fire inside the small community church, killing at least 26 people. Hide Caption 1 of 15 Photos: Sutherland Springs church shooting People comfort each other at a community center near the scene of the deadly shooting. Hide Caption 2 of 15 Photos: Sutherland Springs church shooting Investigators work at the scene. Victims range in age from 17 months to 77 years old.

Hide Caption 3 of 15 Photos: Sutherland Springs church shooting Enrique and Gabby Garcia watch investigators at the scene. Hide Caption 4 of 15 Photos: Sutherland Springs church shooting Law enforcement officials gather near the First Baptist Church. The shooter was killed after a brief chase north into neighboring Guadalupe County, according Guadalupe County Sheriff's Office spokesman Robert Murphy. Hide Caption 5 of 15 Photos: Sutherland Springs church shooting A man wipes his eyes after the shooting. Hide Caption 6 of 15 Photos: Sutherland Springs church shooting Flags are lowered to half staff at First Baptist Church following the shooting. Hide Caption 7 of 15 Photos: Sutherland Springs church shooting Law enforcement officials and forensic experts gather at the scene. Hide Caption 8 of 15 Photos: Sutherland Springs church shooting Emergency personnel seal off the scene of the mass shooting. Hide Caption 9 of 15 Photos: Sutherland Springs church shooting Law enforcement officers man a barricade near the church. Hide Caption 10 of 15 Photos: Sutherland Springs church shooting Carrie Matula embraces a woman after the shooting. Matula said she heard the shooting from the gas station where she works across the street. Hide Caption 11 of 15 Photos: Sutherland Springs church shooting Law enforcement officials work the shooting scene. Hide Caption 12 of 15 Photos: Sutherland Springs church shooting A woman prays with a man after the shooting. Hide Caption 13 of 15 Photos: Sutherland Springs church shooting The FBI responded to the scene of the shooting, according to Michelle Lee, spokeswoman for the FBI's San Antonio field office. Hide Caption 14 of 15 Photos: Sutherland Springs church shooting "My heart is broken," said Wilson County Commissioner Albert Gamez Jr. "We never think where it can happen, and it does happen. It doesn't matter where you're at. In a small community, real quiet and everything, and look at this, what can happen." Hide Caption 15 of 15

Kelley praised Dylann Roof

After Kelley served jail time for the assault and was discharged from the Air Force, Edwards said he reached out to her on Facebook to be a job reference.

"I wanted to help him, and I really wanted him to succeed," said Edwards, who by that time was also out of the military.

But their conversations made Edwards increasingly uncomfortable. At one point, Edwards said, Kelley praised Dylann Roof, the man who entered a South Carolina church and killed nine people during a bible study.

"He would say 'isn't it cool? Did you watch the news?'" Edwards said. "He would say he wished he had the nerve to do it, but all he would be able to do is kill animals."

Kelley was accused in 2014 of punching a dog in Colorado. He initially pleaded guilty to animal cruelty, but the case was dismissed after he paid fines, court documents show.

'You feel like we failed'

After Sunday's shooting in Texas, Edwards got a text from a friend: "Jessika—it was Kelley. The shooter."

"I dropped a glass and started crying," Edwards said.

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While she feels she did what she could for Kelley -- he once thanked her for "having his back" -- she says she's been thinking about those Facebook messages.

After cutting off communication with Kelley, Edwards deleted their conversations and wrote the experience off as Kelley "talking weird like he always did."

"In a sane person's mind, when people say something like that you don't think it's something they're going to do," she said.

After the shooting, Edwards told the FBI about the messages in hopes they can be recovered from Kelley's Facebook account.

Before blocking Kelley from Facebook for good, Edwards said she gave him her phone number and said if he "found himself in a state of mind that he was going to hurt himself or someone else, to call me."

"I told him that," she explained, "because at one point he told me that I was one of the only people... he could talk to that made him feel calm."

Her phone never rang.

"It's upsetting because you feel like we failed," Edwards said. "But in reality we did everything we possibly could do."