An autopsy to determine when and how 20-year-old Iowa student Mollie Tibbetts died is planned for today.
Tibbetts vanished while on an evening jog on July 18. Nearly a month later, a man who confessed to pursuing her as she ran on a country road led authorities to the field where a body believed to be hers was buried under corn stalks, officials said Tuesday.
While authorities have yet to confirm the body is hers, they arrested Cristhian Bahena Rivera, 24, on first-degree murder charges .
Rivera, who's an undocumented immigrant , told investigators he saw her and got out of his car. He ran beside Tibbetts -- even after she warned him she would call police, officials told reporters Tuesday.
The suspect alleged he blacked out at some point . He led authorities to the field Tuesday morning, where they found a body dressed in Tibbetts' clothing and covered in corn leaves.
It is unclear why Rivera killed Tibbetts, said Rick Rahn, special agent in charge at the Iowa Division of Criminal Investigation.
"I can't really speak to you about the motive," Rahn said. "I can just tell you it seems that he followed her and seemed to be drawn to her on that particular day and for whatever reason he chose to abduct her."
An autopsy to determine when and how the woman died is planned for Wednesday.
Authorities had been looking for Tibbetts for about a month when they found home surveillance video that showed a car following a woman running.
After watching it for hours, investigators found clues that led them to Rivera. He didn't resist when authorities tried to detain him, Rahn said.
Authorities believe the suspect has been in the area for four to seven years, Rahn said. Charges were filed in district court in Poweshiek County and bail was set at $1 million. If convicted Rivera could get life in prison without parole. Iowa does not have the death penalty.
President Donald Trump referred to the case while speaking at a rally in Charleston, West Virginia.
"You heard about today with the illegal alien coming in very sadly from Mexico. And you saw what happened to that incredible beautiful young woman. Should have never happened. Illegally in our country," he said. "We've had a huge impact but the laws are so bad, the immigration laws are such a disgrace. We're getting it changed but we have to get more Republicans."
Tibbetts allegedly threatened to call cops
Video recorded by a home surveillance system shows the suspect followed Tibbetts on July 18, authorities said.
According to court documents, the suspect said in an interview that when he approached Tibbetts, she pulled out her cell phone and told Rivera she was going to "call the police" and that caused him to get angry.
He said he blacked out and woke up at an intersection in rural Poweshiek County, court documents say.
Rahn said the suspect told investigators he realized he had put the woman in the trunk of his car and when he took her out, he saw blood on the side of her head, the document says. He left the body in a cornfield and covered it with corn leaves, it adds.
Shawn Neudauer, a spokesman for Immigration and Customs Enforcement, said the agency on Tuesday sent a detainer request to local authorities for Rivera, who is from Mexico. That means ICE could take custody of Rivera if he was released from local custody.
Rahn said Tibbetts' digital footprint, which included data from a fitness tracker known as a Fitbit, played a role in solving the case.
She was dog-sitting before her run
Tibbetts was last seen jogging on July 18 in the small community of Brooklyn, Iowa, about an hour east of Des Moines, according to the Poweshiek County Sheriff's Office.
Before she went missing, her brother dropped her off at her boyfriend's house so she could dog-sit, HLN reported. Her family reported her missing after she did not show up for work the next day.
Investigators launched an extensive search for Tibbetts across the area, including in ponds, fields and from the air.
Tibbetts was studying psychology at the University of Iowa and wanted to get a doctorate and write books, her father said.