An illegal immigrant from Mexico stands accused of killing college student Mollie Tibbetts and dumping her body in an Iowa cornfield — after he allegedly accosted her during a July 18 jog and she threatened to call police. 

Cristhian Bahena Rivera, 24, was charged with first-degree murder Tuesday in Tibbetts' death, officials confirmed. 

Authorities said Rivera, who lived in the rural Poweshiek County area, is being held on a federal immigration detainer.  He's believed to have been in the area for four to seven years. 

The body of Tibbetts, a 20-year-old University of Iowa student, was found Tuesday in a field covered with corn stalks.  Her father and two sources confirmed to Fox News on Tuesday morning that Tibbetts was found dead; investigators said later in the day they were working to formally identify the body. 

MOLLIE TIBBETTS, UNIVERSITY OF IOWA STUDENT FOUND DEAD: A TIMELINE OF EVENTS

Investigators said they used surveillance footage to track down Rivera.  The video showed Tibbetts jogging in a rural area near her hometown of Brooklyn, and also showed Rivera's car.  She was last seen around 7:30 p.m. on July 18 after she went for a jog around a neighborhood in Brooklyn. 

Tibbetts' family pleaded for her safe return and had remained hopeful she would be found alive.  Her father, Rob, previously told Fox News that "somebody knows something." 

Brooklyn, according to her father, is a small city and “you can’t do anything there without someone seeing it.” 

Iowa's Division of Criminal Investigation received more than 4,000 tips during the investigation, and had roughly 30 to 40 investigators working on the case. 

Investigators followed "hundreds" of those leads — interviewing several hundred people and canvassing a nearby hog farm, cornfields and other properties for traces of the college student.  Two items Tibbetts typically took with her — a Fitbit and cellphone — remained missing. 

MOLLIE TIBBETTS, MISSING IOWA STUDENT, FOUND DEAD, HER FATHER SAYS

Investigators announced last week that they were focusing the search on five locations in and around Brooklyn, which included a car wash just a block away from the city’s main commercial strip and a TA truck stop next to Interstate 80, which runs across the entirety of Iowa. 

Brooklyn, a town of just 1,400 people, was shaken by Tibbetts' disappearance.  Blake Jack, the brother of Tibbetts’ boyfriend, told Fox News on Aug. 8 there was no sign of a struggle at the Brooklyn home she was staying in at the time. 

Dalton, Tibbetts' boyfriend of two years, said he believed the doors of the home where his girlfriend last stayed had been left unlocked. 

“It’s Brooklyn.  You don’t lock your doors,” Dalton said. “ We lock our doors now.  Every night.” 

Vice President Mike Pence said he's "heartbroken" about Tibbetts' death, and called the college student an "amazing young woman."  He tweeted that "justice will be served" against the murder suspect. 

"We will never forget Mollie Tibbetts," the vice president added. 

Iowa Gov. Kim Reynolds shared similar sentiments, calling the news about Tibbetts "heart-wrenching," and said that Iowans "are angry that a broken immigration system allowed a predator like this to live in our community." 

"Mollie Tibbetts, our hearts are broken," Republican Iowa Rep. Steve King tweeted Tuesday. " We all prayed for your safe return.  May you now be with the Lord and your family one day find a peace.  Justice must now be served.  RIP Mollie." 

Fox News' Katherine Lam, Lillian LeCroy and Emilie Ikeda contributed to this report.