(CNN) A police investigator who was at the autopsy for two Idaho children found dead months after they went missing testified Monday he took notice at the amount of duct tape used on the boy's body.
In June, law enforcement officials found the remains of Tylee Ryan, 16, and JJ Vallow, 7, on rural property in Fremont County, Idaho, belonging to Chad Daybell, who is married to the children's mother.
The children's disappearance had become national news after Daybell and the mother, Lori Vallow, abruptly left the area after being questioned by police about the whereabouts of the children and about the recent death of Daybell's former wife.
After the children's remains were found in June, Daybell was charged with two counts of conspiring to destroy, alter or conceal evidence.
Authorities have not said how the children died and no one has been charged with killing them.
Rexburg Police Detective Ray Hermosillo, testifying Monday at a preliminary hearing for Daybell, said JJ was buried in a black plastic bag in red pajamas and black socks and with a white and blue blanket on top of him.
Hermosillo said he observed "several layers of duct tape tightly wrapped" around the boy's head, from his chin to his forehead.
JJ also had duct tape wrapped over his elbows, arms and hands, Hermosillo said in court, and his wrists and ankles were bound with the tape.
Daybell's attorney, John Prior, questioned Hermosillo about his recollection of dates and times of key moments in the case.
Monday was the first day of the hearing, which is expected to last two days. The judge plans to rule at the end whether there is sufficient evidence to go to trial.
Another witness, Melanie Gibb, testified that she stayed with Lori Vallow on the weekend in September that JJ was last seen. Gibb said she saw Daybell with Vallow two to four times that time. She and another person were doing a podcast when Daybell's brother came into the room with JJ. It was between 9 p.m. and midnight, she testified.
That was September 22. Tylee was last seen September 8 during a family trip to Yellowstone.
Authorities in June used pings from the cell phone of Vallow's now-deceased brother to pinpoint potential search areas on Daybell's property. The children's remains were found June 9 and 10.
Vallow had already been jailed on two felony counts of desertion and nonsupport of children and three misdemeanor charges. She pleaded not guilty. Last month, prosecutors added the same charges as Daybell, but she has not appeared in court on those counts.
Daybell and Vallow were married in November, a month after his wife, Tammy Daybell, died in her sleep. Authorities are still investigating her death. They initially thought her death was natural, but have since deemed her death suspicious and exhumed her remains on December 11.
Vallow's brother, Alex Cox, died in December.
Gibb said that on November 26, Chad Daybell called her and told her not to pick up when police called. She testified that he explained the police were at Vallow's home asking where JJ was, and Vallow was going to say that he was with Gibb in Arizona. Vallow told her later that day someone was trying to kidnap JJ, she said.
According to body camera footage played in court, Vallow told police JJ was with Gibb and they cannot reach her because she is at a screening of "Frozen 2."
Vallow and Daybell apparently left Idaho after talking with police. Almost two weeks later, Gibb called police in Arizona to tell them what had happened.
The search for the children then intensified.
in January, the couple was found in Hawaii, where they had been since December 1. They were served with a search warrant, and police gave Vallow a deadline to turn JJ and Tylee over to authorities. But that deadline came and went without any sign of the two.
In February, Vallow was arrested, and in March she was extradited from Hawaii.
Her preliminary hearing is scheduled for August 11.
Correction: A previous version of this story gave the wrong age for Tylee Ryan. She was 16 at the time of her death.