The mass shooter who killed 26 people in Texas last Sunday in the worst mass shooting in Texas history bought dogs from Craigslist for use in target practice, according to a report.

Devin Kelley, 26, reportedly purchased the animals via Craigslist with the sole intention of killing them, a former U.S. Air Force colleague told CNN. Jessika Edwards, who served at the Holloman Air Force Base in New Mexico from 2010-12 with Kelley, told the news station the mass shooter was "...using the dogs as target practice."

The former colleague acknowledged she never vetted the veracity of Kelley's claims, but said he told her of his actions via Facebook messages three years ago after reconnecting in civilian life. She told CNN the admission prompted her to end the friendship.

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Edwards said she tried to warn superiors of his dark worldview. When Kelly was disciplined for poor performance, she warned her bosses to "...back off, or he would shoot the place up," she told the news station. Edwards has since been interviewed by the FBI investigating his crimes.

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