A 7-year-old boy with autism and his 17-year-old sister from Idaho have been missing for three months, and the FBI believes they're in serious danger. The children's disappearance could be connected to the death of their stepfather's former wife, investigators said.



The children's mother, Lori Vallow, and stepfather, Chad Daybell, have been uncooperative and have vanished themselves, CBS News national correspondent Errol Barnett reports.

Joshua "JJ" Vallow and Tylee Ryan were last seen in Rexburg, Idaho on September 23. But investigators only discovered they were missing while investigating the death of Daybell's ex-wife.

Tammy Daybell, a librarian in town, died in her home on October 19. She was initially thought to have died of natural causes, but in a later investigation, the local sheriff's office determined her death might be suspicious. Her body was exhumed for an autopsy, and those results are pending.

Chad Daybell got remarried within a few weeks to Vallow and, in the course of the investigation into Tammy's Daybell death, police were made aware of the two children missing in the area. Concerned relatives reached out to police after not hearing from JJ for weeks.

Investigators performed a welfare check at Vallow's home in late November. She and Chad Daybell told police that JJ was staying with a family friend in Arizona, but when investigators returned the next day with search warrants, Vallow and Daybell were gone.

"I don't know why they're doing what they're doing. It doesn't make any sense," said Brandon Boudreaux who, according to local TV station KSTU, used to be married to Vallow's niece and even baptized Tylee.

Boudreaux said Vallow and Daybell have cult-like religious beliefs focused on the end of the world, and he thinks that could have played a role in the case.

"I don't know what happened to those kids. I know that there's people who do, and they're not talking," he said.

Investigators are reportedly also looking into Lori Vallow's ex-husband's and brother's deaths earlier this year. Police are urging anyone who may know the whereabouts of the children to immediately call 911.

"Chad Daybell was a loving husband and has the support of his children in this matter. Lori Daybell is a devoted mother and resents assertions to the contrary," an attorney for Chad Daybell and Vallow said in a statement. "We look forward to addressing the allegations once they have moved beyond speculation and rumor."