Police say a body found Tuesday is that of 20-year-old Mollie Tibbetts, a University of Iowa student who went missing more than a month ago.

And a first-degree murder charge has been filed against 24-year-old Cristhian Bahena Rivera, who authorities say is an undocumented immigrant.

They say Tibbetts was last seen jogging in Brooklyn, Iowa, a small rural town of about 1400 people, and security camera footage helped them identify a car believed to be Rivera's who is in police custody and has been interviewed.

(SOUNDBITE) RICK RAHN, IOWA DIVISION OF CRIMINAL INVESTIGATION SPECIAL AGENT, Saying: "During that interview he tells us that he sees Mollie running and was able to come upon her and approach her, and then at one point he tells us that Mollie grabbed a hold of her phone and said you need to leave me alone I am going to call the police.

And then she took off running, he turned and chased her down and then he tells us that at some point in time he blacks out and then he comes to near an intersection which we believe he then placed Mollie." Tibbetts was reported missing the next day after she failed to show up at a nearby daycare center where she worked.

Authorities say that Rivera led investigators to the body of Tibbetts.

She was found in a corn field in Poweshiek County, not far from where she vanished.

Her disappearance set off a massive search involving the FBI, state agencies and the local community, while her family begged for her safe return.

And about $400,000 dollars were raised for any tip that led to her return.