BROOKLYN, Iowa — Cristhian Bahena Rivera, the Mexican farmworker accused of killing a 20-year-old college student and concealing her body beneath corn leaves, seemed to have built a quiet, productive life in the seven or so years since he slipped across the southwest border and found work in the fields of Iowa.
He tended to dairy cows on a farm owned by a prominent family and returned home each evening to a modest brown trailer along a gravel road outside town.
But Mr. Bahena Rivera’s quiet demeanor sometimes stood out in jarring ways. A neighbor said he did not always follow the local custom of acknowledging him when Mr. Bahena Rivera drove by in a Chevy Malibu. And, more alarmingly, a woman said he made her uncomfortable with a romantic advance and repeated Facebook messages in the middle of the night.
“He would just stare. He wouldn’t really like talk,” said the woman, Brooke Bestell, 20, who had turned Mr. Bahena Rivera down when he asked her out on a date. “Something about him was off.”
Over the course of this week, Mr. Bahena Rivera, 24, went from a quiet farmworker whose real name was unknown, even to his employer, to a homicide suspect whose arrest inflamed the national immigration debate.
President Trump has cited the first-degree murder charge against Mr. Bahena Rivera as proof of the need for tougher border security. Iowa politicians and conservative news outlets have seized on the case as ammunition as November’s election nears. And here in Brooklyn, population 1,400, residents have struggled to understand how the man they saw at the grocery store could be tied to the death of Mollie Tibbetts, a psychology student and summer camp counselor who disappeared last month while out for a jog.
Mr. Bahena Rivera, who is jailed on a $5 million cash bond, was one of many Mexicans who have made their way to Iowa’s pastures, where farmers often struggle to find eligible workers to tend their crops and cattle. Mr. Bahena Rivera grew up in El Guayabillo, a village of unpaved roads some three hours’ drive from Acapulco on Mexico’s Pacific Coast, and attended the only elementary school in the village of about 400 people.
“A very good person, a simple guy with no vices,” Victor Manuel Nuñez Carbajal, who attended school with Mr. Bahena Rivera, said in a Facebook message. Neighbors told Univision network that his father tended his small corn plot and also milked dairy cows in the village, earning less than $10 a day.
Mr. Bahena Rivera came to the United States at age 17, his lawyer said, with the equivalent of a middle school education. After a few years at another farm, he went to work at Yarrabee Farms outside Brooklyn, which is co-owned by Craig Lang, a former Republican candidate for Iowa agriculture secretary.
“I would say he always did his work on time,” Mr. Lang said. “But he wasn’t much for conversation.”
His lawyer, Allan M. Richards, said Mr. Bahena Rivera had been a law-abiding employee since arriving in the United States. “He’s here living the American dream and working seven days a week, 12 hours a day, and trying to do his best at his job,” Mr. Richards said. He said Mr. Bahena Rivera’s family members were not yet willing to speak publicly.
Federal officials said they have no record of Mr. Bahena Rivera entering the country legally and said that he appeared to have used false documents to obtain employment.
The sheriff’s department in Poweshiek County said it had not interacted with him until this week. Neither had any state law enforcement agencies in Iowa.
Mr. Lang said Mr. Bahena Rivera had been hired at the farm in August 2014 after presenting a valid Social Security number, which was checked with a federal database, and a state-issued identification card. The new employee was known around town as Cristhian Bahena Rivera, but around the farm by the fraudulent name listed on those documents, a name the authorities did not disclose.
Outside of work, Mr. Bahena Rivera started dating a Brooklyn high school student, Iris Monarrez, whom he met in 2013. Around 2014, they had a daughter. And for about a year, they lived together. Mr. Bahena Rivera once posted on Facebook that the day he met his girlfriend was “el mejor día de mi vida,” or “the best day of my life.” When she posted a photo of herself in 2015, he wrote in Spanish, “My beautiful cool princess.”
“He was really romantic,” said Aby Felix, a second cousin of Ms. Monarrez, who she said has been separated from Mr. Bahena Rivera for about two years. “He would bring her flowers.”
Residents said Mr. Bahena Rivera was an attentive father who was often seen playing with his daughter in the city park.
His arrest has rattled Brooklyn, a small town where most everybody knows everybody else, and where many had assumed someone from outside the community was responsible for Ms. Tibbetts’s disappearance on July 18.
Ms. Tibbetts, a student at the University of Iowa known as a talented writer, had attended high school in Brooklyn and was known for her frequent jogs around her hometown. After weeks of investigating and national news coverage, police found security video that showed a dark-colored Malibu driving back and forth as she ran on the day of her disappearance. The Malibu was later tied to Mr. Bahena Rivera, who police said cooperated and led them to her body after being taken into custody on Monday.
A medical examiner said Ms. Tibbetts, whose funeral is Sunday, died in a homicide from “multiple sharp force injuries.”
Many here said they felt terrible both for the Tibbetts family and for Ms. Monarrez, who could not be reached for an interview and whose Facebook page has been flooded with vitriolic messages from outside Iowa.
Some in Brooklyn were perplexed by the arrest of a man many knew as a familiar, if unremarkable, face around town. Mary Jo Seaton, a former owner of a Brooklyn grocery store, said he often stopped by her store in the late afternoon or early evening, usually with two other young men she presumed to be his co-workers.
“They would be talking to each other, smiling, laughing, and if you spoke to them or said hi, they would smile back at you,” Ms. Seaton said.
Because they spoke Spanish and most store employees did not, she said, they did not talk at length with staff. “I thought he seemed like a very nice person — a clean-cut, American person,” Ms. Seaton said.
Others found his behavior more troubling. Ms. Bestell, the acquaintance who declined a date with him, said he would not make conversation when she encountered him in person, but he would send repeated social media messages over a period of months.
“Just over and over, like every week or so, he would message me again,” Ms. Bestell said, including as recently as June 13 at 3 a.m.
After he was arrested, two of Ms. Bestell’s friends told her that he had also messaged them online over the years. “I don’t know how many other girls he probably was trying to talk to,” she said.
Ann Klein reported from Brooklyn, Mitch Smith reported from Chicago and Miriam Jordan from Los Angeles. Reporting was contributed by Caitlin Dickerson in New York, Adam Goldman and Ron Nixon in Washington, Elisabeth Malkin in Mexico City and John Peragine in Montezuma, Iowa. Susan Beachy contributed research from New York.