Rivera was employed and resided in Poweshiek County for four to seven years, Iowa Division of Criminal Investigation Special Agent in Charge Richard Rahn said at a press conference in Montezuma on the afternoon of August 21.
Police said Rivera admitted to approaching Tibbetts while she was out running.
Last week, authorities investigating the disappearance said they were focusing on five areas in and near her hometown.
"The bottom line is somebody knows something", Rob Tibbetts, Mollie's father, said previously, adding that Brooklyn is a tiny town and that "you can't do anything there without someone seeing it".
Democrats and immigration advocates have said that by focusing on outlier criminal cases, Republicans and Trump are distorting the fact that immigrants are no more prone to criminal acts than the native-born population - and some studies have found they are actually less likely to commit crimes.
Yarrabee Farms, the Iowa farm that employed the suspect charged with killing Mollie Tibbetts, defended its vetting of Cristhian Bahena Rivera late Tuesday.
Her family reported her missing the following day when she didn't show up for work. He allegedly said he started running alongside her or behind her.
The case will be prosecuted by the Iowa Attorney General's Area Prosecution Division.
The University of Iowa student's last known communication was a July 18 Snapchat message she sent to her boyfriend, Dalton Jack, for whom she was house sitting, according to the Register.
Authorities say Christian Rivera, 24, has been charged with first-degree murder in Mollie Tibbetts ' death.
The body of an adult female was found early Tuesday in a farm field southeast of Brooklyn, approximately two miles from where Tibbetts was last seen jogging on July 18. She took off running and he in turn chased her down.
"You heard about today with the illegal alien coming in very sadly from Mexico", he said.
"It's not the ending we all hoped for at all", friend Alyssa King tells PEOPLE.
Dozens of law enforcement officials from local, state and federal agencies were involved in the investigation after the disappearance of Tibbetts.
Last week, officials announced that they were narrowing their search to five locations in Brooklyn: a vehicle wash, two local farms, a truck stop, and her boyfriend's home. Iowa Governor Kim Reynolds released a written statement Tuesday saying her heart goes out to the family, and that the country's immigration system is at fault. Rivera led investigators to the body, which was covered in cornstalks. "And then he comes to near an intersection which we believe he then placed Mollie", Rahn said.
A body thought to be that of the 20-year-old has been found in Poweshiek County, the area where Miss Tibbetts lived, police confirmed.