A lawyer working for the Rzuceks, murdered pregnant mother Shanann Watts' family, has spoken out in an exclusive two-part interview on 'The Dr. Phil Show' and shared disturbing new details of the day convicted triple murderer Chris Watts strangled Shanann, and their two young daughters to death.

A pre-recorded interview with attorney Steven Lambert appeared on Part 1 of the exclusive on March 5. He alleges in the interview that four-year-old Bella had walked in on her father disposing of her mother's body which was wrapped in a sheet. 

PEOPLE reported that Lambert said in the interview: "Bella walked in and asked, ‘What are you doing with Mommy?'" The attorney then claimed that Watts told his daughter: "Mommy is sick, and we need to take her to the hospital to make her better."

It was at some point after he had this conversation with Bella that the father smothered her as well as three-year-old Celeste. He hid the bodies of his two daughters in oil tanks near his work place and buried his pregnant wife in a shallow grave close by. Their bodies were all discovered three days later.

Watts was sentenced in November last year after he pleaded guilty to all three murders. He is now serving five life sentences without the possibility of parole. The convicted killer was reportedly having an affair with one of his co-workers at the time that he murdered his wife and children. The authorities claimed during the trial that it was his desire to have a "fresh start" with his mistress which was the motive for murdering his family.

According to Lambert, the killings took place after an argument the couple had about Watts' affair. He told Dr. Phil: "In that fight, [Chris] essentially confessed to having an affair, that he wanted a divorce, that it was pretty much over between them. [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."

A statement from the Colorado Bureau of Investigation on February 18 said that the authorities had 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", the statement said. A spokesperson for the CBI told PEOPLE that the office now plans to release the new information on March 7 and added that the office was surprised by the Dr. Phil interview.