BOISE, Idaho — A detective Monday described in excruciating details how investigators unearthed the remains of two children who had been missing for months while searching the rural Idaho property of a man charged with concealing evidence.

The testimony came during a preliminary hearing where a judge will decide whether there is enough evidence to hold Chad Daybell for trial. He and the children’s mother face charges related to the hiding of the remains of 17-year-old Tylee Ryan and 7-year-old Joshua “JJ” Vallow, although authorities have yet to say how the two died, or whether homicide charges will be filed in the case that has attracted worldwide headlines.

Daybell late last year married Lori Vallow Daybell, who’s charged with conspiring to help him keep the bodies of her children hidden. Both have pleaded not guilty in the case that has ties to doomsday beliefs and the mysterious deaths of others close to the couple.

Rexburg Police Detective Ray Hermosillo said “JJ” Vallow’s body was found beneath fresh sod, under which were three large white flat rocks in a row and then a piece of wood paneling. He said the body was buried in a black plastic bag covered in duct tape.

He said when the body was taken to the medical examiner’s office, investigators found a white plastic garbage bag over the boy’s head covered with layers of tightly wound duct tape. Hermosillo said the boy’s wrists and ankles were also bound with duct tape, and that more duct tape bound together his forearms over his chest. The boy was dressed in red pajamas and was wearing black socks.

Hermosillo testified that the girl’s body was found a short distance away. He said they found evidence that the remains appeared to have been burned.

Investigators said they found the bodies by tracking the movements of Lori Vallow’s brother, Alex Cox, using cellphone data. Police say Cox was involved in the conspiracy to hide the children’s remains. He died of an apparent blood clot in his lung at his Arizona home last December.

Court documents in Lori Daybell’s criminal case include claims that the couple believed dark spirits, or “zombies,” would possess people. A friend, Melanie Gibb, said Lori Vallow told her at different times last year that both children had become zombies and that the couple believed the only way to rid a person of a dark spirit was by killing them.