IOWA CITY, Iowa — 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.