Assistant attorney general Scott Brown noted that Rivera is suspected of being in the country illegally, and is charged with a "heinous crime".
The 20-year-old was last seen during an evening jog over a month ago.
The footage reportedly showed a Chevy Malibu connected to Rivera that was driving back and forth as Tibbetts was running in the area.
Mollie's grieving family broke their silence on Wednesday during a vigil at the University of Iowa where she would have entered her sophomore year this fall.
His attorney, Richards, lashed out at President Donald Trump for publicly declaring his client guilty within hours of his arrest Tuesday.
It is not clear when Tibbetts was killed and if she knew her alleged murderer, if all.
A statement from the White House referred to Rivera as an illegal alien. Lang says, "our employee is not who he said he was".
Immigration issues may dominate the 2018 mid-term election.
His attorney, Allan M. Richards, has disputed claims Rivera was in the United States illegally.
However, a study published in 2012 Justice Quarterly found that "foreign-born individuals exhibit remarkably low levels of involvement in crime".
"Carry on her legacy, remember this as a time the country came together for one girl, one girl that loved everyone, one girl that wanted the best for everyone", said Mollie's brother Jake Tibbetts, KGAN reports.
Investigators say Rivera led them to a body believed to be Tibbetts early Tuesday. "It's a city street that turns into county road, with corn fields on both sides", he said. Iowa Governor Kimberly Reynolds released a statement indicating that she had spoken with the family of the victim and hopes that they can "find comfort knowing that God does not leave us to suffer alone".
The system said Rivera's documents checked out, Lang told the press. They said the 24-year-old worked under a different name and was a good employee who helped take care of their cows and got along with co-workers. The Brooklyn-based company said it was shocked to hear that Rivera was charged in Tibbetts' death.
We appreciate the hard work of law enforcement officials.
"Let's let the process go", he said. "Nobody noticed a difference".
Attempts to reach Monarrez on Thursday were not immediately successful.
"Our hearts go out to the Tibbetts family and to the Brooklyn community".
Rivera confessed on Tuesday after police found surveillance footage of him following Mollie in his auto.
Rick Rahn, special agent in charge at the Iowa Division of Criminal Investigation, said the suspect's motive was unclear. "And for whatever reason, he chose to abduct her". Local authorities described him on Tuesday as being undocumented. The next thing he recalled, he told investigators, was being in his auto and finding a headphone earpiece in his lap that did not belong to him. That prompted him to open the trunk, where he saw Tibbetts bleeding from the head. Representatives for U.S. Immigration and Customs Enforcement did not respond on Wednesday to questions regarding Rivera's immigration status.
Even President Trump used it at a West Virginia rally on Tuesday.
"You heard about today with the illegal alien coming in very sadly from Mexico". I think we need immigration laws that focus on people who pose a real threat. Um that's what we're going miss the most.