(CNN) Moments before Amber Guyger killed her neighbor, allegedly mistaking his apartment for her own, the then-Dallas officer was on the phone with her police partner.

But the two didn't have just a professional relationship. Guyger testified that she once had an affair with her married partner, Martin Rivera , one that she later described as "morally wrong."

Dallas police Sr. Cpl. Martin Rivera testified in Amber Guyger's murder trial.

Rivera testified he deleted the texts between him and Guyger from the night of the shooting,

"That's not something that I would want to be reminded of," Rivera said. "And I don't keep messages saved unless it's of an importance to me."

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