Chad Daybell’s former sister-in-law was “shocked” and felt betrayed when he married cult mom Lori Vallow less than three weeks after Tammy Daybell’s death.

Samantha Gwilliam, Tammy Daybell’s sister, is one of several insiders who will speak with Dateline NBC the case that involves the disappearance and death of two of Vallow’s children, 17-year-old Tylee Ryan and 7-year-old JJ Vallow, the deaths of several spouses, and the the quick marriage of Daybell and Vallow after his wife’s sudden death.

The children disappeared in September 2019, but their mother did not report them missing. Tammy Daybell died on October 19, 2019, and Chad Daybell and Lori Vallow exchanged vows on a Hawaiian beach 17 days later.

Family members said Tammy Daybell had been in excellent health and had visited with her siblings and parents just two weeks before she died. Friends said she was training to run a marathon.

“[Chad said] that she’d been sick and had a coughing fit and passed away,” Gwilliam said, recalling the phone call about the death of her sister. “He sounded upset and devastated. I mean, I was crying and he was crying. It was a really hard moment.”

But when Daybell and Vallow married just as suddenly as her sister died, Gwilliam was stunned.

“I was shocked because at that point, Tammy had only been gone for a month,” she said. “I just thought, ‘Is the grief clouding his judgment?’ I mean, who goes and does that? It didn’t make sense to me. And obviously, I was really upset.”

Seventeen days, she thought, “was too soon for anybody to get over my sister.”

Chad Daybell and Vallow are awaiting trial on charges related to hiding the remains of JJ and Tylee, whose bodies were found buried on Daybell’s property in Salem, Idaho. No one has been charged with their deaths, and authorities are investigating whether the couple may have had something to do with Tammy Daybell’s death. Chad refused to allow an autopsy, but authorities exhumed her body in December 2019 but have not released results of the autopsy and toxicology reports.

A string of other deaths have haunted the case, beginning with Vallow’s ex-husband, Charles Vallow, who was shot to death by her brother Alex Cox in July 2019. Cox died in December of that year, but an autopsy determined he died of natural causes. Investigators had reopened the investigation of Charles Vallow’s death at the time of Cox’s death — the shooting had initially been ruled self-defense. Cox was also under investigation for Tammy Daybell’s death and was believed to have helped bury the children’s bodies.

Dateline NBC’s report, “Mommy Doomsday,” airs Friday at 9 p.m. ET.

Read more on the Daybell-Vallow case on CrimeOnline.

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