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BROOKLYN, Iowa (CBS NEWS/AP) – Iowa college student Mollie Tibbetts has been found dead, just over a month after she was reported missing, CBS News has learned. Authorities say they are holding a suspect in her death, and he is being held on a federal immigration detainer.

Investigators identified the suspect as Christian Rivera who is allegedly in the United States illegally.

The 20-year-old was last seen July 18, jogging near her home in the central Iowa town of Brooklyn.

Mitch Mortvedt, an assistant director of the state Division of Criminal Investigations, says Tuesday that authorities are holding a suspect.

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.

s096760829 Suspect In Death Of Mollie Tibbetts In Country Illegally, Official Says

The body was discovered in rural Poweshiek County, the Iowa Division of Criminal Investigation said in a news release. So far, no details have been released about what the cause of death might be.

There is heavy police activity in rural Poweshiek County, just south of Interstate 80 near Iowa Highway 21, CBS affiliate KCCI-TV reports.

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.

The Associated Press contributed to this report. This is a developing story and will be updated.

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