IOWA CITY, Iowa (AP) - The Mexican man charged with abducting and killing an Iowa college student was known for years on the dairy farm where he worked by another name: John Budd.

The alias has emerged as Cristhian Bahena Rivera’s employer, a cattle operation owned by a prominent Republican family, faces questions over whether its managers were aware of any warning signs that he was in the country illegally.

The name under which Rivera was hired and paid for the last four years was confirmed by three people with knowledge of his employment history. They spoke on condition of anonymity because they were not authorized to release the information during an ongoing criminal investigation. One of the people said Rivera’s work identity as John Budd appears in official government records.

The employer, Yarrabee Farms, declined to confirm or deny Rivera’s work identity. Lori Chesser, an immigration employment lawyer advising the farm, said that companies cannot discriminate against workers based on how they look or how their names sound.

Farm officials have said Rivera presented an out-of-state photo identification and a Social Security number when he was hired in 2014, and they believed he was the person depicted in those documents until his arrest last month.

The farm followed legal requirements to examine the documents and determined “that they appeared genuine on their face and related to the person presenting them,” Chesser said. “Questioning a name or other characteristic would violate the anti-discrimination provisions of the law.”

During his four years at the farm near the small town of Brooklyn, Iowa, Rivera “was called and responded to the name he used in the hiring process,” Chesser said. He lived in a trailer owned by the farm as a benefit of his employment, as do about half of its 10 workers.

The farm did not use the government’s voluntary E-Verify system, which allows companies to confirm the identity and eligibility of employees to work in the U.S. Farm manager Dane Lang has apologized for a mistake in falsely claiming to have used E-Verify in an initial statement on Rivera’s Aug. 21 arrest, hours after he allegedly led police to Mollie Tibbetts’ body in a nearby cornfield.

It’s unclear whether E-Verify would have detected any red flags with Rivera’s claimed identity, but the farm has said it used a different government service to confirm that the name and Social Security number matched.

Police say Rivera followed and confronted Tibbetts while she was out for a run on July 18 and later stabbed her to death. He has been jailed on $5 million bond while awaiting trial on a first-degree murder charge, which carries a sentence of life in prison. The federal government has also filed an immigration detainer, which means he would be subject to deportation proceedings if acquitted.

Immigration and Customs Enforcement declined to comment on whether the agency is investigating Yarrabee Farms, which has said that it received dozens of angry phone calls after Rivera was arrested.

Tibbetts’ father, Rob Tibbetts, has urged the public not to bring his daughter’s death into the divisive racial debate over immigration.

“The person who is accused of taking Mollie’s life is no more a reflection of the Hispanic community as white supremacists are of all white people,” he wrote in an opinion piece for the Des Moines Register.

Employers typically do not face legal consequences for hiring a worker under false documents as long as they were not involved in obtaining them and had no other obvious reason to suspect they are fraudulent, said Bob Teig, a retired federal prosecutor in Iowa.

“Absent unusual circumstances, it would be difficult to show they knew any more than what they were told,” Teig said, adding that it would be “pretty racist” to assume a John Budd could not be Hispanic.

Whether anyone else knew Rivera as John Budd is unclear. The 24-year-old had a Facebook page under his real name, and his account listed many friends from the central Iowa area. He has a girlfriend and a young daughter, his former attorney has said.

Rivera had neither an Iowa-issued identification under any name nor any known criminal history or interactions with police. It’s unclear who owned the car that he allegedly used to circle Tibbetts.

Rivera’s former defense lawyer, Allan Richards, has accused the farm and other employers in the area of turning a “blind eye” to the reality that many of their workers are in the U.S. illegally and employed under false documents. He has said that Rivera came to the U.S. when he was around 17 and has the equivalent of a middle-school education.

Erica Johnson, an advocate who directs the American Friends Service Committee’s immigration program in Iowa, said the case highlights the “precarious position” that immigrant workers and their employers face.

“We have an immigration system that doesn’t account for the labor needs or economic realities of Iowa businesses and farms,” she said. “So what do you do? Do you rightly not racially profile people and take the information they give you because you need workers?”