Immigration enforcement agents and state criminal investigators on Thursday visited the Iowa dairy farm that employed and housed the man charged with killing college student Mollie Tibbetts.

Agents from Immigration and Customs Enforcement, the Iowa Division of Criminal Investigation, and the county sheriff's office spent two hours at Yarrabee Farms in Brooklyn, Iowa, on Thursday morning. They appeared to be looking around the property and talking to workers.

Yarrabee Farms said that it is cooperating with federal authorities who had asked to visit the farm. The company confirmed in a statement that investigators met with employees and owners for two hours, but it said it could provide no additional details due to an ongoing investigation.

Division of Criminal Investigation spokesman Mitch Mortvedt that his agency's officers were on the scene assisting investigators from the Department of Homeland Security and ICE, who took the lead. Mortvedt said that means the activity was focused on federal law and not the homicide case, which his agency is leading. An ICE spokesman declined comment.

The visit came one day after The Associated Press reported that the suspect in Tibbetts' death, Cristhian Bahena Rivera, worked at the farm for years under a false identity, John Budd.

Rivera was arrested and charged with first-degree murder last month in the stabbing death of Tibbetts, 20, who vanished while out for a run in Brooklyn on July 18. Investigators say Rivera, a 24-year-old native of Mexico who came to the U.S. during his teenage years, was in the U.S. illegally and is subject to deportation proceedings.

The farm has said that at least a couple of its roughly dozen employees left the area following Rivera's arrest, which sent fear through the immigrant community. The dairy, which has about 800 cows and is owned by a prominent family with Republican Party ties, says it received dozens of angry phone calls and some death threats.

Rivera, 24, worked there for roughly four years and lived in one of its trailers for free. The farm has said that about half of its workers live in provided housing.

Farm managers have said Rivera presented an out-of-state identification and a Social Security number when he was hired in 2014, and that they were unaware of his true identity until his Aug. 21 arrest. The company did not use the government's voluntary E-Verify system to check his identity and eligibility to work, although it's unclear whether that would have made a difference.