Lori Vallow Daybell secretly recorded saying dead son was "safe and happy"

In a December 2019 phone call that she secretly recorded, Lori Vallow Daybell's best friend, Melanie Gibb, confronted her about the whereabouts of her 7-year-old son JJ.

The Final Days of JJ and Tylee
The Final Days of JJ and Tylee 42:35

Last Updated Oct 4, 2020 2:08 AM EDT

CBS News correspondent Jonathan Vigliotti and "48 Hours" go inside the investigation into the heartbreaking national search for two missing children in "The Final Days of JJ and Tylee."

When news broke in December 2019 that 7-year-old JJ Vallow and his 16-year-old sister, Tylee Ryan, were missing from Rexburg, Idaho, their mother, Lori Vallow Daybell, became infamous as the "cult mom" who refused to tell anyone where they were.

While several police departments and the FBI conducted a nationwide search for her children, she jetted off to Hawaii with her new husband, a former gravedigger turned author, podcaster and doomsday prophet, Chad Daybell. This strange true-life drama — which including Chad and Lori's alleged beliefs in zombies and the nearing end of times — would take its darkest turn just six months later, when authorities found remains of both children buried in unmarked graves in Chad Daybell's backyard.

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Lori Vallow-Daybell and JJ Vallow at Yellowstone National Park on September 8, 2019. FBI

"This crime is horrendous. What happened to those kids is horrendous." investigative reporter and CBS News consultant Morgan Loew told "48 Hours." "It was heartbreaking, it was infuriating, and it just made people want to know why. Why did this have to happen?"

Investigators believe only Lori and Chad can answer exactly what happened to JJ and Tylee, but neither has cooperated with police. Both are now in jail awaiting trial for conspiracy to destroy, alter or conceal evidence for their roles in disposing of the children's bodies. A secret recording played at Chad Daybell's preliminary hearing this past August appears to provide evidence of how the couple engaged in a cover-up. It is a story that centers around Lori's best friend, Melanie Gibb. 

"Melanie Gibb is critical to this investigation," says Morgan Loew. "Melanie Gibb was the key to getting Lori arrested to begin with."

It all started on November 26, 2019, when the Rexburg Police Department conducted a welfare check for JJ. When confronted by investigators, Lori told them he was with Melanie in Arizona. After authorities left, Melanie says she received a call from Chad Daybell telling her not to answer when police tried to reach her. That was followed by a call from Lori. Melanie testified that Lori asked her to lie and tell police that JJ was with her and that she had taken him to a movie.

Melanie testified, "She asked me just to pick up my phone and … take a picture of random kids to make it look like it was JJ."

Melanie says she felt uneasy after the conversation with Lori ended.

"I was not OK with it because she told something to the police that was not true," Melanie testified. "I had a really bad feeling in my stomach, and I felt very shooken (sic) up by it."

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Tylee Ryan, 17 and JJ Vallow, 7, at Yellowstone National Park on September 8, 2019 -- the last time Tylee was seen. At right is their mother's brother Alex Cox.   FBI

Melanie was so bothered by what had happened that over the next couple of weeks she began to feel that JJ might be in danger, and that Lori and Chad could be the ones responsible. So, on December 8, she confronted them on the phone. She secretly recorded the call, which has become a key piece of evidence.

"That taped phone conversation is when you can hear Chad and Lori go from, 'Oh, yeah, everything's great,' to that change where, 'OK, we've got a problem here,'" says Morgan Loew.

"Is JJ safe?" Melanie asks at one point in the call.

"He is safe and happy," was Lori's response.

"We know that they knew that the kids were not alive at that point," Morgan told "48 Hours." "We know that they knew that those kids were not OK. We know they were lying when they said the kids were fine."

Melanie remained skeptical, and as the 2-minute phone call continues, you can hear as Lori tries her best to pull her back into the fold.

"I love you with all my heart, and I have forever, and I will always love you," Lori can be heard in the recording.

"I appreciate those words, but if you really love me, you wouldn't have told the police that I had JJ with me," was Melanie's response. "That's not what a friend does"

Melanie Gibb immediately turned the tape over to police. It was not long before authorities announced JJ and Tylee were missing and that their lives could be in danger.