VIDEO: How police got Chris Watts to change his story about killing his wife, daughters

Perhaps the most revealing thing about the hours of interrogation tapes from the questioning of Chris Watts is the sense that Colorado detectives never really believed the North Carolina native's story about what really happened to his missing wife and daughters.

In the videos recorded during two days in August inside the Frederick Police Department in Colorado, Chris Watts admits to detectives that his marriage was in trouble, he was having an affair and says he told his wife the morning she disappeared that he was leaving her.

Watts' wife, Shannan, was raised in Aberdeen. The couple met in North Carolina before moving to Colorado to raise their daughters, 4-year old Bella and 3-year old Celeste.

"Obviously it's getting pretty emotional," Watts tells detectives, describing the early morning conversation with his wife. "We're talking about we felt the disconnection was there. We're falling out of love."

The lead detective expresses skepticism about the story, "The day (Shannan) goes missing is the day you guys have marital discord," he said. "You can understand what I'm thinking about you."

At this point in the interview, Watts maintains his innocence, "It honestly just makes me sick to my stomach because this is something that I would never do," Watts claims. "There's no way I would harm anybody in my family at all. I am telling you the absolute truth."

But one day later, Watts' story changed after detectives tell him that he failed a lie detector test.

"It is completely clear that you were not honest during the testing," a detective tells Watts. "And I think you already know that. You did not pass the polygraph test."

Police bring in Watts' father to the interrogation room where the son tells his dad that Shannan strangled the girls.

"They were, they were blue," Watts tells his father.

When detectives returned, Chris Watts version of the truth was that Shannan killed their daughters and when he discovered what she did, he killed Shannan in a rage.

"The evil that I saw when I walked behind Shannan when she was behind (Celeste)," he said. "I didn't know what to do. I didn't know what to (expletive) do. None of this made sense!"

That turned out to be a lie as well.

Watts ultimately admitted in court that he killed Shannan and his daughters then dumped their bodies in a Colorado oil field.

He'll spend the rest of his life in prison -- after he pleaded guilty earlier this month.