The Chevy Malibu that investigators linked to Cristhian Rivera, the illegal immigrant suspected of killing Iowa college student Mollie Tibbetts, was not registered in Rivera's name, a law enforcement source revealed to Fox News on Wednesday.

Police said Tuesday that the Malibu, which was caught on surveillence footage in Brooklyn, Iowa, was driving back and forth in the area where Tibbetts, a 20-year-old University of Iowa student, was running in the "late afternoon hours of July 18," the day she went missing.

"We were able to, first of all, see what we believed to have been Mollie running on one of the streets," Iowa Division of Criminal Investigation special agent Rick Rahn told Fox News. "From that, we started to look into all the vehicles that were also captured on video and eventually identified the vehicle that was driven by Mr. Rivera."

The surveillance footage in which the Malibu was seen was not able to capture the vehicle's license plates, but there were "unusual markings" on the car which helped lead investigators track it down, Rahn told said.

The special agent said there were "some distinct features to the vehicle that allowed us to basically search the area for it and just happened that we were able to locate the vehicle, and subsequently identify Mr. Rivera driving the vehicle."

MOLLIE TIBBETTS, UNIVERSITY OF IOWA STUDENT, FOUND DEAD: A TIMELINE OF EVENTS

The footage was provided by a resident. It clearly showed Tibbetts running, and also had a clear shot of the Malibu driving back and forth, Rahn told Fox News. The video was "critical" and allowed authorities to zero in on the 24-year-old Rivera, Rahn added.

Rivera was charged with first-degree murder on Tuesday in Tibbetts' death, and was being held Wednesday on a $5 million cash-only bond. During his first court appearance Wednesday afternoon, Rivera looked stoic and refused to speak when given the chance. Rahn said authorities believe this was a "premeditated" attack.

While investigators earlier had looked into the area where Tibbetts' body was ultimately discovered — a cornfield roughly 12 miles southeast of Brooklyn — Rahn said detectives wouldn't have seen the woman's body even if they were relatively close, as it was covered in cornstalks.

He wouldn't detail what led investigators to the Deep River Area where Tibbetts' body was found, but stressed that they "focused hard on her digital footprint."

Investigators said they were working to determine whether Rivera acted alone. They said that other charges may be filed against Rivera if evidence shows that sexual assault or other crimes were committed against Tibbetts.

Immigration and Customs Enforcement (ICE) agents said that Rivera, of Mexico, has been in the U.S. illegally for four to seven years.

Yarrabee Farms, which had hired Rivera, initially said he passed a federal E-Verify check, which is intended to maintain a database of I-9 forms and tax records of employees across the country. On Wednesday, however, co-owner and manager Dane Lang said that the farm used a different program that a family member wrongly thought was E-Verify. The farm used Social Security Administration data in the vetting process, Lang said.

Lang added that Rivera provided a state-issued photo ID and social security card.

“We learned that our employee was not who he said he is," Lang told reporters on Wednesday, and noted that his coworkers knew him by a different name, but recognized him after seeing media reports about his arrest.

A spokesperson with U.S. Citizenship and Immigration Services said in a statement that, "A search of records by USCIS revealed Rivera did not make any DACA requests nor were any grants given. We have found no record in our systems indicating he has any immigration status."

Despite what federal officials have stated about Rivera's status in the U.S., his lawyer said the suspect worked legally in the country.

Attorney Allan Richards alleged that the government was saying falsely that Rivera was not in Iowa legally, in a court document through which he asked for a gag order on the case, the Des Moines Register reported.

A judge denied Richards' gag order request.

Fox News' Melissa Chrise contributed to this report.