Transcript for Girlfriend of man who admitted to killing family: 'He lied about everything'

The Colorado father pleaded for the return of his wife and daughters even though authorities say he had already killed them. And tonight, the mistress who said he was divorcing, breaking the silence here is linsey Davis. Reporter: Week after Chris Watts pleaded guilty to murdering his daughters and pregnant wife Shannan, his girlfriend, is pulling back the curtain on a double life. Daddy is my hero -- Reporter: Nichol Kessinger telling "The Denver post" Watts is "A liar, he lied about everything." They met at work just weeks before his family went missing, she says he told her he was finalizing a divorce. And described him as "Soft spoken" and a "Good listener." But his story unraveled when his family went missing and he begged on TV for their return. I just want them back. Reporter: Kessinger telling the post, "I thought, 'if he was able to lie to me and hide something that big, what else was he lying about?" When she pressed him for answers his lack of emotion only made her more suspicious and she feared for his wife and children. Police recovering their remains at a Colorado oil site. His daughters hidden in inside storage tanks. Reporter: She says she wanted to help and went to investigators while police were still searching. Watts is expected to get life in prison. David? Thank you.

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