SALT LAKE CITY — Interviews with children and phone pinging helped law enforcers in northern Utah find the body of a missing woman who was allegedly murdered.

The body of Merrilee Cox-Lafferty, 37, was found Sept. 14 in a shallow grave in Left Hand Fork Canyon. She had driven to northern Utah on Aug. 17 from California with her minor daughter and was last seen on Aug. 18. She was reported missing on Aug. 21.

After her body was found, Stacy Robert Willis, 41, of Hyrum, was arrested and later charged in 1st District Court with capital murder, a first-degree felony; three counts of obstructing justice, a second-degree felony; possession of a dangerous weapon by a restricted person, a second-degree felony; two counts of drug possession, a class B misdemeanor; possession of drug paraphernalia, a class B misdemeanor; and criminal mischief, a class B misdemeanor.

With a capital murder charge, Willis could face the death penalty if convicted. Prosecutors have not said yet whether they intend to pursue that. Willis has been ordered by a judge to be held without bail in the Cache County Jail. His next scheduled court date is Oct. 1.

According to a newly unsealed search warrant, Cox-Lafferty traveled to Utah from California with her daughter to deliver drugs to Willis.

"Merrilee was bringing two large bags of marijuana from California to give to Rob to sell, so her mom could get money," the daughter told police in a Sept. 3 interview, according to the warrant.

Logan Police Capt. Curtis Hooley on Wednesday confirmed that drugs were a factor in the investigation, but he said detectives were still unsure why Willis allegedly turned on Cox-Lafferty. He said the two had known each other for a number of years.

Willis initially told police that he and Cox-Lafferty got into a heated argument in the parking lot of an apartment complex on Aug. 18.

"Rob said that Merrilee was yelling and swearing profusely," according to the warrant. "Rob said because of the fight he was four hours late for work."

A friend of Willis' told police he had to take his children inside because of the argument and that "he told Rob to tell Merrilee to stop because she would cause issues for him at the apartment complex," the warrant states.

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But when police interviewed those children on Aug. 24, "none of them (recalled) this argument occurring in their presence," according to the warrant. Officers asked other tenants at the complex about the alleged fight and questioned those who Willis and his friend specifically said heard it.

"None of the persons contacted during this canvass recalled seeing or hearing the dispute as described by (the friend) and Rob," the warrant states. "Even these specifically identified individuals did not recall the dispute."

Willis claimed that Cox-Lafferty continued to text him after he went to work, to the point that he blocked her number on his cellphone, the warrant states. But when a police officer asked to see the messages, Willis "stated the call logs and messages between him and Merrilee after their fight in the parking lot were deleted when he blocked her number on his phone," according to the warrant.

Willis also claimed he eventually called emergency dispatchers to report Cox-Lafferty missing, but they told him that a person needed to be gone for 24 hours before he could file a report, the warrant states.

"Local public safety dispatch shows no record of Rob's phone number contacting dispatch. Your affiant also spoke with dispatch supervisors who explained it is not policy or practice for dispatchers to tell anybody wishing to report a person missing there is a 24-hour prerequisite," the officer who attempted to verify Willis' story noted in the warrant.

On Aug. 19, Willis drove Cox-Lafferty's daughter to a mutual friend's house in Mountain Home, Idaho, to have a woman there take care of the girl, the warrant states.

When police interviewed the daughter, she said she had seen her mother at Willis' house in Hyrum on Aug. 18. But because the two were arguing, "she didn't want to be there and asked to be taken back" to the friend's house, the warrant states.

Logan police originally announced that the discovery of Cox-Lafferty's therapy dog, that had been picked up and turned into a local shelter, was a big turning point in the investigation. Police obtained surveillance video of Willis and his friend arriving at work on Aug. 18. In the video, the men have Merrilee's Australian shepherd mix with them, according to the warrant, but there is no sign of Cox-Lafferty.

Investigators also "pinged" Cox-Lafferty's cellphone in an attempt to retrace her steps. A ping from Aug. 18 at 1:30 p.m. placed her phone in the area of Blacksmith Fork Canyon, the warrant states. A second ping about 45 minutes later placed the phone west of the intersection of 1700 South, U.S. 89/91, in Logan, near the road.

The warrant, which was written before Cox-Lafferty's body was found, was written to investigate the possible crime of homicide. The officer who wrote the warrant noted that both Willis and his friend, "have made materially false statements regarding their activities on Aug. 18, 2018."

As of Wednesday, the friend had not been arrested or charged. Hooley said, however, that "other people are being considered" as part of the ongoing investigation. When completed, the case will be turned over the Cache County Attorney's Office, which will determine what charges, if any, should be filed, he said.

Cox-Lafferty's vehicle was located in Boise and search warrants have been issued in Idaho and Utah.

Willis was convicted of felony discharge of a firearm in 2014 after firing two shots at a couple trying to pull out of a Walmart parking lot in North Logan. He was sentenced to one to 15 years at the Utah State Prison.

Utah court records show that Willis also has convictions for forgery in 2003, escape from custody in 2000 and possession with intent to distribute a controlled substance in 1999.

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