Two children not seen since September and feared to be in "serious danger" were allegedly never reported missing by their mum or her partner.
Idaho police searching for Joshua Vallow, 7, and Tylee Ryan, 17, want to speak to their adopted mum and her new husband who they say have repeatedly lied about the children's whereabouts.
Mum Lori Vallow, 46, and husband Chad Daybell, 51, married just weeks after the latter's first wife died mysteriously in her sleep with police now treating the death as potentially suspicious.
Tammy Daybell died in Springville, Utah, in October and her body was exhumed on December 11 to allow for an autopsy to be conducted.
Vallow is also a widow with her brother Alex Cox having recently shot her previous husband Charles Vallow, claiming it was self-defence.
With police investigating that death, Cox himself then died.
Joshua has special needs and the disappearance of him and his sister are understood to be linked to the death of Tammy.
The whereabouts of Vallow and Daybell are unclear as they fled their Rexburg home. Officers were then issued with warrants to search locations associated to Daybell.
While investigating the death of Tammy, police learned of the disappearance of the two kids.
A welfare check was attempted on Joshua on November 26 as family members claimed he had not been seen for weeks.
Vallow lied that he was staying with a family friend in Arizona and police do not believe the children were with their mum or Daybell when they fled.
Joshua last went to school at Kennedy Elementary in Rexburg on September 23.
Joshua has brown eyes and brown hair. He is 4' tall and weighs 50lbs.
Tylee has blonde hair and blue eyes. She is 5' tall and weighs 160lbs.
Vallow has blonde hair and blue eyes and is 5'6".
Daybell, 51, has brown hair and blue eyes and is 6'3".
Assistant Chief Gary Hagen, of the Rexburg Police Department, said: "We've received numerous false statements from them advising that the children were with family members of friends.
"We're deeply concerned about the children and their safety... We would even be good with a FaceTime video of the children to make us feel better that they are safe."
Anyone who has seen either child since September is asked to call 208-359-3000 or 1-800-THE-LOST (843-5678).
