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FREDERICK, Colo. — Chris Watts had just strangled his wife Shanann and was wrapping her in a sheet to dispose of her body when their daughter Bella walked into the room.

“What are you doing with mommy?” the 4-year-old asked her father.

The details of that interaction — Bella’s last known words before her death — and more information about the disturbing familial murders were revealed by Steven Lambert, the attorney for Shanann Watts’ family, on the “Dr. Phil” show Tuesday.

Lambert’s comments provide a chilling picture of how Chris Watts killed his pregnant wife Shanann, 34, and their two children, Bella and Celeste, 3, and then disposed of their bodies at a secluded oil field where he worked.

Prosecutors said he strangled his wife with his bare hands, suffocated the children, and then loaded their bodies in his vehicle and drove away to hide their remains.

He initially denied involvement in the August disappearance of his wife and daughters, and even spoke with local media about his worry for their well-being.

However, he later pleaded guilty to the killings and was sentenced in November to five life sentences after prosecutors and Shanann’s family agreed to drop the possibility of the death penalty.

Lambert is with Greeley law firm Grant & Hoffman. He told Dr. Phil that the children were alive as Watts drove to the remote oil field where he worked and dumped Shanann’s body in a dirt pile.

“He walks over, takes Cece’s favorite blanket from her and smothers her. He takes her body out of the vehicle. At this point, Bella unbuckled herself and she said, ‘please do not do to me what you just did to Cece,'” Lambert told Dr. Phil.

Lambert said this information was provided to Sandra Rzucek, Shanann’s mother, following the Feb. 18 prison interview. Lambert said the confession was “extremely painful, but important to have answers.” He also said the family was “relieved” because it ends any speculation that Shanann had anything to do with the kids’ deaths. Chris Watts originally claimed he killed her in a fit of rage after she killed the girls.

Lambert told Dr. Phil that he believes Chris Watts is showing remorse and has reportedly found God while in prison.

RELATED: Complete coverage of murders of Shanann Watts, daughters

The TV interview comes a week after Colorado Bureau of Investigations spokeswoman Susan Medina said Watts provided investigators with “additional information” about the murders of his family on Feb. 18.

The CBI said a written report and audio file from that interview will be released Thursday.

After his sentencing in November, prosecutors had said they might never know what led Watts to kill his wife and daughters.

“I don’t think he will ever tell us. I don’t think he will give an honest assessment of why he did what he did, how he did what he did,” Weld County District Attorney Michael Rourke said.

But in the “Dr. Phil” interview, Lambert said the couple got into a fight and Chris Watts confessed he was having an affair.

He also said he wanted a divorce and declared their relationship was over.

“And she had 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,” Lambert said.

As Watts began to wrap her body up in a sheet, Bella walked in and asked about her mother, Lambert said.

“She’s 4, what we’ve been told she’s quite smart — was quite smart — and knew something likely was up. And what he said was that, ‘Mommy is sick, we need to take her to the hospital to make her better,'” Lambert said.

The “Dr. Phil” episode also features video of Chris Watts watching a neighbor’s surveillance tape of him backing up his truck and putting something in the back.

As Watts watches that surveillance tape, he puts his hands on his head, and the neighbor later notes he was acting fidgety.