The mistress of the Colorado man who pleaded guilty to killing his wife and two daughters is giving has spoken out with her side of the story.

Kessinger told the Denver Post she was shocked when she learned about Shanann and the girls' disappearance in August.

According to Business Insider, she met Watts at her job, working for a contractor for Anadarko Petroleum.

Kessinger recalls finding him "soft-spoken" and attractive, and says he told her he was in the middle of divorcing his wife.

Kessinger says their relationship turned physical at the beginning of July, when they began seeing each other four to five times a week.

On the day of Shanann and the girls disappearance, Watts called her and said that his wife had taken off with his kids, but seemed eerily calm.

That night on the news, Kessinger found out that not only were Watts and his wife still married, but his wife was 15 weeks pregnant.

I thought, 'If he was able to lie to me and hide something that big, what else was he lying about?'

Watts was eventually arrested after the bodies of the girls were found dumped in oil tanks, and their mother buried in a shallow grave nearby.

Initially, Watts admitted to killing his wife, saying he only attacked her because he caught her strangling one of their daughters.

He's a liar. He lied about everything."

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