BROOKLYN, Iowa — Investigators continued Thursday to delve into the background of Cristhian Bahena Rivera — the 24-year-old suspected of killing college student Mollie Tibbetts — as his relatives expressed disbelief at what police said unfolded in this quiet stretch of Iowa.

Tibbetts disappeared after going for a jog on July 18, setting off a weeks-long search in the area. Authorities charged Rivera, a Mexican national and farmworker, with first-degree murder. They said he is an undocumented immigrant, a revelation that thrust the case into the center of the country’s knotted political debate.

Preliminary autopsy results released Thursday determined that Tibbetts’s death was a “homicide resulting from multiple sharp force injuries.” In court filings, police said Rivera confessed to pursuing her and admitted to dragging her body from his car to a cornfield, where it lay hidden for more than a month.

People who knew Rivera in Iowa and Mexico were at a loss to explain the situation.

“I don’t know what’s going on,” his uncle, Eustaquio “Capi” Bahena Radilla, said in an interview Thursday conducted through an interpreter at his trailer home in Brooklyn. “I don’t know what’s happening because honestly, I know he’s a good person.”

Rivera’s father echoed his comment, saying Thursday that he believed that his son was innocent and calling reports of his confession “pure lies.”

“If he had done what they say he did, he would have come back here [to Mexico],” Eduardo Bahena Radilla, his father, said in a telephone interview from Guayabillo, a small town in Mexico. “But he’s innocent, so he didn’t run and hide.”

Tibbetts was missing for a little more than a month, during which the search for answers increasingly agonized her family, who pleaded with the public for help in finding her.

Rivera’s relatives and his employer said that, as police searched the area for Tibbetts, Rivera’s behavior didn’t change and he gave no indication that he knew what happened to the missing woman. Rivera’s father, a 43-year-old farmer, said he last spoke to his eldest child on Friday, a few days before Rivera’s arrest.

“He seemed calm,” Bahena said. “I didn’t sense anything was wrong.”

According to a court affidavit,  Rivera told authorities that he had parked his car and followed a woman running in Brooklyn. When she threatened to call the police, he “panicked and got mad,” but does not remember what happened next, the affidavit states.

Rivera’s next memory, authorities wrote, is in his car realizing that the woman was in his trunk, where he found her with blood on the side of her head. After police questioned him, Rivera guided law enforcement officials to a cornfield where they found Tibbetts’s remains, the affidavit said.

So far, authorities said they have not found anything indicating that Tibbetts and Rivera knew each other before the attack. But some people in the small city of Brooklyn — home to fewer than 1,400 people — were shocked to learn they were connected to both the woman who went missing and the man charged with killing her.

Chloe Reding, 19, was good friends with Tibbetts in junior high; they drifted apart in high school but became close since graduating, sometimes packing into a car to drive around.

Tibbetts was active in a group chat with Reding and some of their friends, but she went quiet while she was missing, which began to cause concern. When Reding turned on the televised news conference, she was shocked to realize she recognized the man arrested for the crime.

“I was watching it with my mom and I kind of freaked out,” Reding, a nursing assistant, recalled of the moment she saw police identify the suspect as Rivera. “I was like, ‘Oh my god, I know him. I’m pretty sure I’m friends with him on Facebook.’ ”

Reding said she “didn’t personally know him” but added, “It’s just small-town Brooklyn, you now?”

Around his 16th birthday, Rivera left Guayabillo to find work in the United States, his father said.

“There are no jobs here, so he left,” Bahena said, adding that his son crossed the border illegally and was undocumented in the United States.

He settled in Iowa because his uncle was already living there, Bahena said. He found work on a series of milk farms and often sent money back to his parents in Mexico.

“He said it was pretty” in Iowa, his father recalled. “I think he liked it.”

His uncle, Eustaquio Bahena, said the 24-year-old is a responsible, hardworking and “simple” man who did not drink or do drugs.

Rivera has a 3-year-old daughter with a woman he married and separated from earlier this year, Eustaquio Bahena said. When Rivera had time off work, his uncle said he would spend time with his daughter, bringing her to Eustaquio Bahena’s house to jump on the trampoline with the other young children.

Rivera’s immigration status has drawn more attention to the case, prompting repeated comments from President Trump, the White House and conservative commentators. In a break from when they said it was too soon to discuss policy in the aftermath of mass shootings in Las Vegas and Sutherland Springs, Tex., last year, Trump and his White House have linked Tibbetts’s death to his calls for stricter immigration policies.

During an interview on “Fox & Friends” broadcast Thursday morning, Trump responded to a question about Tibbetts by calling her “this beautiful young girl … killed by a horrible person that came in from Mexico, illegally here,” and went on to refer to his proposed border wall and desire for new immigration laws.

Eustaquio Bahena said he hasn’t spoken to Rivera since the arrest. He said their family is devastated by what happened and deeply sad for Tibbetts’s family. Other members of Rivera’s family attended his first appearance in court on Wednesday, including an aunt and uncle that live in a neighboring town, Rivera’s three-year-old daughter and the child’s mother, according to Eustaquio “Capi” Bahena Radilla.

Still, Rivera’s uncle said that if he did it, he should be punished.

“I want justice to be done,” he said. “It’s clear to me that whoever committed that crime has to pay, whoever they are. … They have to pay for it, whoever they are, even if they are my family.”

Tibbetts’s family has released a statement asking to be “allowed the time to process our devastating loss and share our grief in private.”

Her aunt, Billie Jo Calderwood, said: “Please remember, Evil comes in EVERY color.”

Reding, Tibbetts’s friend, said that she had seen outrage building online over claims that Rivera is undocumented, but that she hasn’t focused on it.

“For some people, they do view it as him being illegal,” she said. “For me, I just see it any race, any sexuality, any person could have done this. It doesn’t matter if he’s illegal or black or white. A lot of people are saying ‘Build the wall’ and all that, but I don’t believe that’s the problem necessarily. Bad people are just bad people.”

Miller and Berman reported from Washington. Alice Crites, Julie Tate and Cleve R. Wootson Jr. contributed to this report, which has been updated since it was first published. 

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