After a Utah college student vanished, cellphone data led detectives to a patch of soil in a mountain gorge

Mackenzie Lueck touched down at Salt Lake City International Airport after midnight on June 17, back from her grandmother's funeral in California.

Instead of returning to the University of Utah, where she was a kinesiology major and a member of the Alpha Chi Omega sorority, she hailed a ride in a Lyft car and directed the vehicle up Interstate 15 to a park in North Salt Lake, about 20 minutes northeast of the airport.

She was dropped off at Hatch Park just before 3 a.m., pulling a brown suitcase, a black backpack and a large blue purse from the vehicle and depositing her luggage in a car that was waiting for her at the public plot boasting tennis courts, picnic tables and a walking trail, authorities would later say.

She climbed in with an unidentified driver.

Three days later, her father reported her missing to the Salt Lake City Police Department, setting off a search for the 23-year-old, who was expected to graduate next year.

"It could have been a male or a female," an assistant police chief said last month, referring to the driver waiting to whisk Lueck away at the public park. "We've exhausted all avenues of determining that information and want to ask this person to please call us."

The attempt to locate the missing woman involved studying surveillance images and phone records and pursuing more than 100 tips, with the help of the FBI.

What authorities found instead, in a vast canyon that cuts through the Bear River Mountains, was Lueck's charred body, which they said had been burned after she was bludgeoned to death. Her arms were bound behind her back with zip tie and rope. A 5-centimeter hole had been bored into the left side of her skull, and part of her scalp was missing.

Those details were revealed by prosecutors on Wednesday, marking the latest grim chapter in a case that authorities say turned from a disquieting disappearance into a ghastly homicide.

Gaps remain in the account of the student's death offered by law enforcement, who say that their investigation is ongoing.

Responsible for the death, prosecutors allege, is the 31-year-old man who met Lueck at the park in the early-morning hours of June 17.

Ayoola Ajayi, an information technology specialist, was held without bail last week and formally charged Wednesday with aggravated murder, aggravated kidnapping, desecration of a human body and obstruction of justice. The Salt Lake Legal Defender Association didn't immediately return a request for comment.

Ajayi could face the death penalty if convicted.

Sim Gill, Salt Lake County's district attorney, said it was premature to discuss sentencing. "That is a possibility that is here," he said at a Wednesday news conference.

Gill, who has championed therapeutic justice and alternatives to prosecution, became emotional when discussing the case, which has captured national attention amid an outpouring of grief from Lueck's family and friends.

His voice broke as he conveyed the appreciation of the young woman's parents for the "support and the prayers that have helped them through this very difficult time."

"They are genuinely appreciative and moved by the outpouring of love and compassion," the district attorney said.

Charging documents give greater insight into the circumstances of Lueck's death, while leaving many questions unanswered. Among them are what Ajayi's motive is alleged to have been, as well as how the two individuals are said to have known one another.

Lueck was described by friends as effervescent and attentive, throwing a birthday party for her cat, Nova, that included champagne. Her sorority sisters came to her defense after a writer from the incendiary Barstool Sports blog, who was subsequently fired, published a piece joking about Lueck's disappearance and discussing her reported use of dating apps.

Ajayi is a Nigerian immigrant who was pleasant to visitors who rented out his room on Airbnb, a roommate told the Los Angeles Times.

But he was also trailed by conflict.

He was banned from Utah State University in 2012 over suspicion that he had stolen an iPad from campus.

Two years after that, a co-worker told police that Ajayi had sexually assaulted her, but charges were never filed, according to the Salt Lake Tribune.

An ex-wife told local television that she had cut off contact with the 31-year-old after he threatened her.

Beyond traffic tickets, Ajayi has no criminal record in Utah.

Last year, Ajayi self-published a novel, titled "Forge Identity," in which characters are burned alive.

A contractor told the Deseret News that Ajayi had contacted him this spring about building a soundproofed room in his home that would feature hooks high on concrete walls.

The contractor, Brian Wolf, said he turned down the request and later contacted police when he learned that his would-be customer was being investigated for murder.

Gill, speaking to reporters on Wednesday, would not elaborate on how the two had established contact, or how long they had been communicating.

He said cellphone records indicated that they had exchanged several messages in the early morning of June 17.

Lueck sent her last message at 2:58 a.m., according to charging documents, and then powered off her phone at 2:59 a.m. Ajayi's phone placed him back at his residence - a modest, clapboard house about five miles south of the park - at 3:07 a.m.

Later the same day, next day, neighbors encountered a "horrible smell" emanating from Ajayi's backyard, they would later tell detectives, according to an affidavit.

When first contacted by police, Ajayi said he had exchanged messages with Lueck but denied meeting her, according to authorities.

A search warrant executed on June 26 led investigators to what appeared to be a freshly dug site behind his garage, court documents allege, where they discovered a human bone, charred muscular tissue, part of a scalp with hair, a cellphone and other burned items. The muscular tissue matched a DNA profile of Lueck, according to the documents.

Neighbors spoke of the noxious odor, and said that they had observed Ajayi pouring gasoline on the fire.

Detectives seized the suspect's car, according to the affidavit, and discovered a red gasoline can. They later determined that he had purchased a similar can at a supermarket on the morning of June 17, they said.

Police took Ajayi into custody at gunpoint on June 28.

Charging documents filed Wednesday state that additional analysis of the suspect's phone records placed him, on the afternoon of June 25, near Logan Canyon, a gorge in the Bear River Mountains almost 100 miles north of Salt Lake City.

On July 3, law enforcement trekked to the canyon. After an extensive search, they located a "disturbed area of soil under a grove of trees," Gill said. Under the soil, they found a charred human body, samples from which matched Lueck's DNA profile.

A state medical examiner found that she had died from bleeding in her skull and ruled her death a homicide.