DES MOINES (CBS News/AP) — Authorities said on Tuesday that they have charged a man living in the U.S. illegally with murder in the death of an Iowa college student who disappeared a month ago while jogging in a rural area.

Authorities say Christian Rivera, 24, has been charged with first-degree murder in Mollie Tibbetts ‘ death.

Investigators say they used surveillance video in tracking down Rivera. The video showed Tibbetts, 20, jogging in a rural area near her hometown of Brooklyn as well as Rivera’s car.

According to CBS News’ David Begnaud, Rivera first spotted Tibbetts while she was jogging.

A 24yo man in the U.S. illegally is charged with killing 20yo Mollie Tibbitts, in Iowa.

The suspect saw Mollie jogging.

He stalked her, then killed her, according to police, after she threatened to call police on him.

The suspect led police to a body believe to be Mollie. pic.twitter.com/OUpfNKGyZf — David Begnaud (@DavidBegnaud) August 21, 2018

“He stalked her, then killed her, according to police, after she threatened to call police on him,” according to Begnaud. The suspect led police to a body believe to be Tibbetts .

Police announced the charge at a press conference just hours after they found what they believe to be the body of Tibbetts in a field covered with corn stalks.

Her family reported her missing the following day when she didn’t show up for work. Her disappearance set off a massive investigation and weeks of fruitless searches.

While hundreds of people have been interviewed, no suspects have been publicly identified in Tibbetts’ disappearance.

Last week, authorities said they were focusing their investigation on five areas in and near Tibbetts’ hometown. Those locations reportedly included her boyfriend’s home in Brooklyn, a car wash, a truck stop, a farm more than three miles from downtown Brooklyn, and another farm more than six miles away. Police asked anyone who was in those areas July 18 to report anything suspicious they may have seen.

In an interview earlier this month, Mollie Tibbetts’ father said he believed his daughter may have left willingly with someone she knew.

“I think someone went to the house that Mollie knew or that Mollie trusted and that she left with them willingly,” Robert Tibbetts told CBS News correspondent Adriana Diaz. “Now they’re in over their head and they don’t know what to do.”

He says if he could talk to his daughter, he would tell her to “hang on.”

“We’re gonna come get you,” he said. “Everybody’s looking.”

More than $385,000 was raised for a reward for Mollie’s safe return. Greg Willey of Crime Stoppers of Central Iowa tells the Associated Press the fund will now likely be used for any information that helps police catch whoever is responsible for her death.

Tibbetts would have started her junior year at the University of Iowa this week.

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