Chris and Shanann Watts had a fight about his affair the night of her death, according to Steven Lambert, a lawyer for the Watts family

Chris Watts Killed Wife After She Threatened to Divorce Him, Take Kids Because of His Affair

Shanann Watts had known about her husband Chris’ affair prior to her death.

A lawyer for the Watts family, Steven Lambert, spoke with Dr. Phil McGraw in a pre-recorded interview during which Lambert shared new details of the murder of the pregnant Colorado mom and her daughters Bella, 4, and 3-year-old Celeste.

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In a clip of the interview obtained exclusively by PEOPLE, Lambert, who is representing Shanann’s family in a wrongful death suit against Watts, recalls a fight between Chris and Shanann.

“In that fight, [Chris] essentially confessed to having an affair, that he wanted a divorce, that it was pretty much over between them,” Lambert tells McGraw. “[Shanann] said something to the effect of, ‘Well, you’re not going to see the kids again.’ As a consequence of that conversation, he strangled her to death.”

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Lambert also reveals that Chris and Shanann’s eldest child witnessed their mother’s murder.

“Bella walked in and asked, ‘What are you doing with mommy?'” Lambert says.

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After killing Shanann, Watts then smothered his two daughters. He then loaded their bodies into his truck and hid them on an oil work site where they were found three days later.

In November, Watts pleaded guilty to all three killings. He is currently serving five life sentences without the possibility of parole.

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Watts was having an affair with a co-worker at the time of the killings. Authorities have cited his desire for a “fresh start” with his mistress as his motive for the killings.

A Feb. 18 statement to PEOPLE from the Colorado Bureau of Investigation says that authorities “interviewed Christopher Watts for the purpose of developing further insight into the case. Watts provided investigators with additional information about the murders of Shanann, Bella, and Celeste during the interview.”

A spokeswoman from the Colorado Bureau of Investigation tells PEOPLE the office plans to release more information on the case Thursday, adding that the office was taken by surprise by the Dr. Phil interview.