Aug. 21 (UPI) -- Iowa officials charged a 24-year-old man with murder after finding what they believed to be the body of college student Mollie Tibbetts on Tuesday.
Cristhian Bahena Rivera faces one count of first-degree murder for the death of 20-year-old Tibbetts, who disappeared July 18 after going out for a nightly run in Brooklyn, Iowa, said Rick Rahn, Iowa Division of Criminal Investigation special agent in charge.
Rahn said surveillance video helped investigators track down Rivera, who led them to the female body in a cornfield.
"Through that we were able to identify a vehicle that we believe belonged to Mr. Rivera," Rahn said. "From that we were able to track his patterns and the routes that he took. We were also able to find Mollie running on this video and we were able to determine that he was one of the last ones to have seen Mollie running."
Rivera said he saw Tibbetts running and decided to follow her and run alongside her on the night of her disappearance.
Rivera told investigators he chased Tibbetts after she grabbed her phone, said "I'm gonna call the police" and then ran away. He said he then "blacked out" and regained consciousness at an intersection outside Brooklyn.
According to an affidavit, Rivera said he didn't realize he had Tibbetts' body in the trunk of his car until he drove to a field entrance and into a cornfield driveway, ABC News reported.
After seeing blood on the side of Tibbetts' head, Rivera said he dragged her body into the cornfield and left her in corn leaves.
Rahn said an autopsy on Wednesday will provide details about the time and cause of Tibbetts' death, but couldn't provide other details regarding the case, including the motive.
"I can just tell you that he followed her and seemed to be drawn to her on that particular day. For whatever reason he chose to abduct her," he said.
DCI Assistant Director Mitch Mortvedt said Rivera was an undocumented immigrant and is believed to have lived in the area for four to seven years.
"What we based everything off of as far as saying he is an illegal alien is we worked with Homeland Security Investigations and they have him as an illegal alien," Mortvedt said during a news conference. "DCI doesn't work immigration stuff so anytime this stuff comes up we defer to them."
Tibbetts' father, Rob Tibbetts, confirmed to Fox News the body belonged to his daughter.
She had been house-sitting for her boyfriend, Dalton Jack, in Brooklyn, about an hour east of Des Moines.
Tibbetts' mother, Laura Calderwood, said her computer, wallet and driver's license were found at the home of Jack, who was cleared as a suspect. Her cellphone, Fitbit wristwatch and earbuds had not been recovered.
The search for Tibbetts was extensive, and at one point led investigators to a pig farm in Guernsey, Iowa, about 11 miles away from Tibbetts' last sighting.
An agent with the Iowa Division of Criminal Investigation said last week authorities received more than 1,500 tips and conducted more than 500 interviews in the case.