BOISE, Idaho >> A detective today 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. Rexburg Police Lt. Ron Ball wrote in court documents that Cox was involved in the conspiracy to hide the children’s remains. Cox 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.

The strange case began last summer after Cox fatally shot Lori Vallow’s estranged husband, Charles Vallow, in suburban Phoenix in what he asserted was self-defense. Vallow had been seeking a divorce, saying Lori believed she had become a god-like figure who was responsible for ushering in the biblical end times.

A short time later, she and the kids moved to Idaho, where Chad Daybell lived. He ran a small publishing company and had written many fiction books about apocalyptic scenarios loosely based on the theology of The Church of Jesus Christ of Latter-day Saints. Friends said he claimed to be able to receive visions from “beyond the veil.”

At the time, Chad Daybell was married to Tammy Daybell. She died in October of what her obituary said were natural causes. Authorities grew suspicious when he married Lori Vallow just two weeks later. Police had Tammy’s body exhumed last December in Utah for further investigation; the results of that autopsy have not been released.

Police began searching for Tylee and JJ in November after relatives raised concerns, and they soon discovered that both children were last seen in September. Police say the Daybells lied to investigators about the children’s whereabouts before quietly leaving Idaho. They were found on Kauai months later.

The case has drawn so much attention that Madison County Prosecutor Rob Wood recently hired a public relations firm to handle the influx of media requests. Authorities have not given details on exactly what they believe happened to the children.

Chad Daybell’s defense attorney, John Prior, also will get a chance to argue his side during the hearing, that is expected to continue Tuesday. Neither the couple nor their lawyers have spoken publicly about the case.

In most preliminary hearings, defense attorneys try to show the judge that prosecutors’ evidence is not strong enough to justify sending the case to trial.