The Federal Bureau of Investigation is assisting local authorities in eastern Idaho as they search for two missing children and two adults wanted for questioning in their disappearance.

The case could also be connected to the death of a woman who may have passed away under suspicious circumstances.

Tammy Daybell, 49, was found dead in her Fremont County, Idaho home on Oct. 19. At the time, she was believed to have died of natural causes, according to a statement from the Rexburg Police Department, and her body buried three days later in Utah.

However, the investigation led authorities to believe that Daybell's death may have been suspicious. On Dec. 11, her remains were exhumed and an autopsy was conducted.

During the course of the death investigation, authorities were made aware that two Rexburg children were missing.

Joshua Vallow, an adopted 7-year-old who has special needs, and 17-year-old Tylee Ryan are the children of Lori Vallow, a Rexburg resident who married Chad Daybell -- the surviving husband of Tammy Daybell -- within weeks of his late wife's death.

Because extended family outside Idaho had not been able to speak with Joshua since September, authorities conducted a welfare check on the boy Nov. 26 at Vallow's home in Rexburg.

During that welfare check, Vallow told police officers that Joshua was staying with a family friend in Arizona. After investigators left Vallow's home, they learned that Joshua had not in fact been staying with the friend Vallow mentioned.

The next day, in an effort to locate Joshua, police officers executed search warrants at multiple locations in Rexburg associated with Vallow. Investigators determined that Vallow and Chad Daybell had abruptly vacated their home and left Rexburg. That's when the police department requested assistance from the FBI.

"Further investigation has determined that Lori Vallow and Chad Daybell did not appear to have Joshua with them when they left Rexburg," the police department said last week.

Joshua last attended school at Kennedy Elementary in Rexburg on Sept. 23. Tylee Ryan has also not been seen since September, and it turned out that none of the children's extended family members have had contact with them since then.

"Additionally, the children have not been reported missing to any law enforcement agency, and attempts to obtain the cooperation of Lori Vallow and Chad Daybell in locating the children have been unsuccessful," police said.

Joshua Vallow is described as a white male with brown hair and brown eyes. He stands four feet tall and weighs 50 pounds. He may go by the nickname "JJ," and may be in need of medical attention.

Tylee Ryan is a white female with blonde hair and blue eyes. She stands five feet tall and weighs 160 pounds.

Chad Daybell and Lori Vallow, Courtesy: Rexburg Police Department

Lori Vallow is 46 years old, stands 5'6" tall and weighs 125 pounds. She has blonde hair and blue eyes. She may now be using Daybell's last name.

Chad Daybell is 51 years old, stands 6'3" tall and weighs 230 pounds with brown hair and blue eyes.

Anyone with information on the missing children is asked to contact the Rexburg Police Department at 1-208-359-3000 or the National Center for Missing and Exploited Children at 1-800-THE-LOST.

Anyone with information on the suspects is asked to contact the Rexburg Police Department or nearest FBI field office.

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