24-year-old Cristhian Rivera, the man who has been accused of kidnapping and killing Mollie Tibbetts in Brooklyn, Iowa, appeared at his arraignment on September 19 and pleaded not guilty. He entered the not guilty plea to a charge of first-degree murder with the help of a translator at a court in Poweshiek County. Chad Frese, his attorney, said in the court that Rivera has a "limited understanding of English and limited education". The 20-year-old college student vanished in July after she went out for her evening run and a massive search was launched to try and find her. Rivera was found out to be the suspect after surveillance footage from homes on the route that Tibbetts took on her run showed his vehicle following her.

Rivera was arrested and he confessed to killing her and led the police last month to the spot in a cornfield where her body was buried. The Iowa State Medical Examiner said in a preliminary report of the autopsy that the student's body revealed that her death had been a "homicide resulting from multiple sharp force injuries". CNN reported that Rivera answered "yes" at his arraignment when the decision was being made to waive his right to a trial within 90 days.

Rivera, a Mexican native who was in the country illegally, is scheduled to appear in court for his trial on April 16, 2019. After the hearing came to an end, Rivera was seen talking to his translator and attorney for a brief moment before he was led out of the courtroom. The man was dressed in a black-and-white striped jail jumpsuit and he looked around at everyone in the courtroom as he was being taken away.

At the hearing that took place before, Allan Richards, another defense attorney for Rivera, told the court that he had come to the country as a minor and held down a job in the community. He also said that his client did not have any previous criminal records. The 24-year-old man is said to have worked at a nearby farm, Yarrabee Farms, for the past four years. When he applied for the job at the farm, he gave the owners a state ID and a Social Security card. Co-owner and manager of the farm, Dane Lang, said that the card had been verified using the Social Security Administration's verification system. 

He also said that the forms had been false and the ID did not identify the man as Rivera. Lang said: "What we learned in the last 24 hours is that our employee was not who he said he was." On September 19, it had been confirmed that Rivera's "true and correct name" was Cristhian Bahena Rivera. Lang also said that Rivera was in good standing as an employee and came to work on time every day as well as having a good relationship with his coworkers. Lang said that he and the other employees never noticed anything suspicious about the worker's behavior after the student disappeared.

In the arrest affidavit, Rivera said that he remembered getting angry with Tibbetts but that whatever happened after that had been "blocked" from his memory. When he finally became aware, he realized he had just put Tibbetts, who had been bleeding, into his trunk. The document states that Rivera then carried her into a cornfield and buried her there. After he was arrested, he took the authorities to the spot where they found Tibbetts' body covered in corn leaves. Her clothes were also found in the same spot.