Rivera made his initial court appearance Wednesday on a charge of first-degree murder in the death of Tibbetts, a 20-year-old University of Iowa student.
For years, his employer said the young man from Mexico presented himself as a legal US resident and reliable worker at a family dairy farm in small town Iowa. That information was run through the Social Security Administration's employment-verification system and checked out, he said.
Rivera's defense attorney, Allan Richards, has denounced Trump for prejudging his client's guilt, saying the president's comments would make it hard for Rivera to get a fair trial. While investigators were confident then that the body was that of Tibbetts, the autopsy definitively confirmed her identity.
Rivera sat stone-faced through much of the hearing, wearing a striped jail jumpsuit, handcuffs and speaking only briefly through a Spanish-speaking interpreter.
President Donald Trump and other leading Republicans have argued that this case shows the need to maintain stricter border security and kick out undocumented immigrants. "Should've never happened. Illegally in our country". Threats have included burning down buildings and even killing their dog after learning Rivera was employed at the farm.
"This is a scary situation", he said.
Yarrabee Farms, owned by a well-known family in Iowa ag, initially said they had gone through the proper legal channels to hire Rivera.
"Something about him was off", said a 20-year-old Iowa woman who turned him down for a date.
A criminal complaint alleges that Rivera confessed during a lengthy interrogation that began Monday to following Tibbetts in his vehicle, getting out on foot and chasing after her. Rivera told investigators that he panicked after Tibbetts threatened to call police on her cellphone, he blacked out and later came to when he was unloading her bloody body from the trunk of a auto, it says. He told authorities that he blacked out and then dumped her bloody body in the secluded location.
"Sharp force injuries" are those caused by pointed or sharp-edged objects, such as in stab wounds, incised wounds and chop wounds, according to the medical news site Medscape.
Investigators said they believed Rivera had lived in the area from four to seven years. It's about a three-hour drive from the resort city of Acapulco.
Authorities said Bahena Rivera and Tibbetts have no known connection beyond that he allegedly told investigators that he had seen her running previously. He faces life in prison without the possibility of parole if convicted.