Cristhian Bahena Rivera had been working at Iowa's Yarrabee Farms for four years under a fake name

Cristihian Bahena RiveraCredit: Poweshiek County
Credit: Poweshiek County

Cristhian Bahena Rivera, who has been charged in the murder of Mollie Tibbetts, worked at a dairy farm less than three miles from where she was seen running the night she vanished.

The manager of the dairy farm that employed the immigrant from Mexico expressed the shock he felt after learning that Rivera had been accused of killing the 20-year-old college sophomore.

“Our employee is not who he said he was,” Dane Lang, manager of Yarrabee Farms in Brooklyn, Iowa, told the Associated Press.

Rivera, 24, had been working at the farm for four years under a fake name, according to the AP.

Mollie Tibbetts

Lang, who only learned on Tuesday that Rivera had been charged, said his employee continued coming to work after Tibbetts disappeared on July 18.

“Nobody saw a difference,” said Lang, who explained that Rivera presented an out-of-state government-issued photo identification and a matching social security card when he was hired in 2014.

On the dairy farm, Rivera helped take care of the cows on a daily basis and was known to be “reliable” by his co-workers. “He was an employee in good standing,” Lang added.

Rivera “kept to himself” and had lived in the area between four and seven years, state authorities said Tuesday.

WATCH: Missing Student Mollie Tibbetts’ Dead Body Found in Local Field More Than a Month After She Vanished: Source

“This is a profoundly sad day for our community. All of us at Yarrabee Farms are shocked to hear that one of our employees was involved and is charged in this case. On Monday, the authorities visited our farm and talked to our employees. We have cooperated fully with their investigation,” Lang said in a statement obtained by ABC News on Tuesday. (Yarrabee Farms is owned by Craig Lang, a prominent Iowa farmer and political figure who lost a GOP primary in the race for state agriculture secretary.)

Lang also stated that his farm did not use a federal E-Verify check on Rivera despite the company’s previous claim that it did.

Also on Tuesday, PEOPLE obtained arrest warrant affidavit which states Rivera is the one who led investigators to Tibbetts’ dead body, where he had allegedly concealed it with plants.

The affidavit also shows Rivera’s alleged explanation for Tibbetts’ death: how he said he pursued her while she was out for her regular evening jog and then later found her body dead in his trunk, her head bloody.

Rivera allegedly said that he had “blocked” himself from remembering the time between — “which is what he does when he gets very upset,” according to the arrest affidavit.

Tibbetts was last seen alive the night of July 18 and, according to Rivera’s arrest affidavit, she was spotted on her run at one point about two and a half miles from Yarrabee Farms.

A car authorities linked to Rivera was also seen in that area multiple times around the same time Tibbetts ran through, the affidavit states. He allegedly admitted to police that he crossed paths with her before her murder.

Rivera was arrested this week and charged with first-degree murder. He is being held in lieu of $5 million bond.