The Mexican immigrant accused of murdering University of Iowa student Mollie Tibbetts used another person's name and identification to get a job on a family farm owned by a prominent Iowa Republican, the owners of the business said Wednesday.

The revelation came after murder suspect Cristhian Bahena Rivera made his first court appearance and was ordered held on $5 million cash bond.

"What we learned in the last 24 hours was that our employee was not who he said he was," Dane Lang told reporters gathered at Yarrabee Farms in Brooklyn, Iowa.

Lang co-owns the farm with his father, Craig Lang, who is a former GOP candidate for the state’s agriculture secretary. He said he knows Rivera by a different name — which he declined to divulge.

"It was not Cristhian," Lang said.

Lang said that when Rivera applied for a job four years ago at the farm, he produced an Iowa state ID and a Social Security card that they checked out by calling the Social Security administration — not the government-run E-Verify system as they had said in an earlier statement.

After it was revealed that they had employed an undocumented worker, Lang said they received more than 100 hostile messages, including death threats and "threats to kill my dog."

Rivera, 24, did not enter a plea during his brief appearance in the Poweshiek County courthouse one day after he was charged with first-degree murder in connection with the death of the 20-year-old Tibbetts.

Wearing what appeared to be a bulletproof vest underneath his black- and white-striped prison outfit, as well as headphones to hear a Spanish-language interpreter, Rivera nodded his head and answered "Si" when asked if he understood the purpose of the hearing.

The judge then denied a motion by Rivera's defense attorney, Allan Richards, for a gag order — and to bar the media from proceedings. In a court document, Richards said comments about the case by President Donald Trump would "poison the entire possible pool of jury members."

"The government has weighed in at the highest levels with a predisposition that my client is guilty," he said.

Rivera, who did not enter a plea, faces life in prison without parole if convicted of killing Tibbetts. Her body was found Tuesday in a field on a farm east of her Brooklyn, Iowa, hometown.

Richards told the court that Rivera was a minor when he moved to Iowa from Mexico.

In a court filing from Richards seeking a gag order in the case, Richards said that the government has been promoting the idea that Rivera is in the country illegally — Trump mentioned the case at Tuesday’s rally in West Virginia — and that "the Government's position of promotion of this idea will prevent any notion of Cristhian's right to a fair trial."

"Sad and Sorry Trump has weighed in on this matter in national media which will poison the entire possible pool of jury members," Richards wrote in the court document. The document appears to rely on an earlier statement from Craig Lang that the farm had verified Rivera was in the Iowa legally — but that was made before the Wednesday afternoon news conference.

In the earlier statement, the Lang brothers had said Rivera was an "employee in good standing."

"This individual has worked at our farms for four years, was vetted through the government’s E-Verify system," it said. "On Monday, the authorities visited our farm and talked to our employees. We have cooperated fully with their investigation."

Investigators used surveillance video to track down Rivera, who was seen following Tibbetts in his car as she jogged on a rural road.

"I can’t speak about the motive. I can just tell you that it seemed that he followed her, seemed to be drawn to her on that particular day, for whatever reason he chose to abduct her," DCI Special Agent Rick Rahn told reporters at a news conference on Tuesday.

"He told us he had seen Mollie in the past and on that particular day, July 18, 2018, he happened to see her, he was drawn to her, and as a result, kind of followed her around a little bit and ultimately confronted her," Rahn said. "And ended up tackling her and ultimately abducting her."

The case has sparked renewed calls for reforming an immigration vetting system that critics say does little to prevent undocumented workers from illegally getting jobs in the U.S.

E-Verify is run by the U.S. Citizenship and Immigration Services, which is part of the Department of Homeland Security. It's described on the site as a voluntary "web-based system that allows enrolled employers to confirm the eligibility of their employees to work in the United States" by matching information provided by workers on the I-9 form against Social Security and Department of Homeland Security records.

But critics like Alex Nowrasteh of the libertarian-leaning Cato Institute dismissed the E-Verify system as a "total joke" that enables undocumented immigrants to get jobs in the United States — and enables employers to keep from knowingly hiring them.

E-Verify accepts Social Security cards, passports and other documentation as proof of identity — but it relies on employers to determine whether the documents submitted by potential employees are legit and not borrowed or stolen, he said.

"E-Verify has been sold as this silver bullet solution to our immigration problems, but none of its supporters have dealt with the systematic inability to weed out illegal immigrants," Nowrasteh said in an interview with NBC News. "Cracking down on illegal immigration is very expensive and can hurt the economy, but politicians have to say they’re doing something about it. E-Verify is a way for politicians to have their cake and eat it, too."

Some states like Iowa have strengthened their E-Verify procedures by enrolling in the RIDE program, which enables an employer to verify the identity of an applicant who presents an Iowa driver’s license or ID card.

But Rivera had neither, said Andrea Henry, a spokeswoman for the Iowa Department of Transportation.

Rivera's next court appearance is set for Aug. 31.