Crime Lori Vallow and Her Husband Chad Daybell Were 'Like Gasoline and Fire,' Says Former Friend Couple charged in children's disappearance were "equally destructive to each," Lori Vallow's former friend Melanie Gibb says in a new Dateline NBC By Jeff Truesdell Published on June 19, 2020 01:30 PM Share Tweet Pin Email Lori Vallow and Chad Daybell were a combustible couple long before authorities searching for her two missing children found the kids' bodies last week on Daybell's property, her former friend says. "I saw him as the hand, and her as the puppet on that hand," the friend, Melanie Gibb, tells Dateline NBC for an episode airing Monday. "They were both like gasoline and fire -- equally destructive to each other." "So in a way, they both had deception in them, and they both lie," she contends. "And so, that was the common thread, is that they were really good lying to each other. [It] seemed like a good fit, for them to be like that with each other." A clip from the episode is above. Bodies Found on Chad Daybell's Property Belonged to Children, Prosecutors Say Vallow and Daybell, who bonded over Daybell's writings on religious doomsday scenarios and were married last November, are jailed in Idaho as authorities continue to investigate the deaths of 7-year-old Joshua "J.J." Vallow and his sister, 17-year-old Tylee Ryan, both of whom were last seen in September. Joshua “J.J.” Vallow, at left, and Tylee Ryan. Rexburg Police Department (2) Vallow, who was arrested in February, is charged with felony counts of desertion and nonsupport of dependent children, resisting or obstructing officers, criminal solicitation to commit a crime, contempt of court and willful disobedience of court process or order for failing to produce the children during the search for them. She has pleaded not guilty. Daybell, who was arrested June 9 after the bodies were discovered, has been charged with two counts of destruction, alteration and concealment of evidence. He has pleaded not guilty. Lori Vallow and Chad Daybell's Families Speak Out After Discovery of Missing Children's Remains The two also are under investigation for potential murder, attempted murder and conspiracy charges in the Idaho county where Daybell lived with his previous wife, Tammy, at the time Tammy died two weeks before Daybell and Vallow were married last November. Confirmation of that investigation was made public in an April 9 letter from the Idaho attorney general’s office to the Fremont County Prosecutor’s Office, in which the AG’s office agreed to assist the local prosecutors in their investigation of those possible crimes. No charges against either Vallow or Daybell have been filed in connection with that investigation. Chad Daybell, at left, and Lori Vallow Daybell. Eric Grossarth/ EastIdahoNews.com Police in Rexburg, Idaho, began to search for J.J. and Tylee last fall, acting out of concern raised by J.J.'s out-of-state grandparents. Want to keep up with the latest crime coverage? Sign up for PEOPLE's free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases. J.J., an adopted boy with autism, had moved with his sister and mother to Idaho from Arizona after the July 2019 shooting death of Lori's previous husband, Charles Vallow, by Lori's brother Alex Cox, who claimed self-defense and was not charged. After the move, the grandparents, Kay and Larry Woodcock, "had a little bit of contact with J.J. in particular, but it became less frequent, and Lori was starting to be non-responsive to the family," Rich Robertson, a private investigator hired by the Woodcocks, tells PEOPLE. Spurred by the grandparents, police made a welfare check on the children in November, only to be told by Lori, "They're staying with my friend down in Arizona, a woman named Melanie Gibb," according to Robertson. "So then we contacted the Gilbert, Arizona, police department and asked for a welfare check on the kids at Melanie Gibb's house," he says. Police who made that contact relayed to him that Gibb said the children weren't there -- and that Gibb claimed she'd received a call from Vallow and Daybell, asking her to lie about the kids' whereabouts. Rexburg police say they documented several inconsistent statements from Vallow and Daybell about the children's whereabouts during the search for them. "That part was huge," says Robertson. "At that point, that's when the press release went out from the Rexburg police department about 'endangered children' and things just started tumbling from there." "What Happened to J.J. and Tylee?" airs Monday on Dateline NBC (10 p.m. ET).