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Running through the quiet rural roads of Brooklyn, Iowa was always 20-year-old Mollie Tibbetts' time for herself.
“She would always put her phone on do not disturb when she was running because that was her-time,” Tibbetts’ cousin Morgan Collum said in the premiere episode of “Dateline: The Last Day,” streaming on Peacock Tuesday.
It was how the University of Iowa college student could unwind after a long day.
But when Tibbetts laced up her running shoes on the night of July 18, 2018 and set out on the familiar roads after leaving her boyfriend’s home, she never realized the run would be her last.
Tibbetts’ disappearance garnered national headlines and launched a frantic search to try to find the 20-year-old, who was working that summer as a counselor at a local children’s day camp.
For more than a month, investigators chased down one false lead after another until a closer look at Tibbetts’ final hours provided them with the clue they needed to unravel the mystery.
Tibbetts spent the day of July 18, 2018 like she had so many other days that summer at the camp where she worked at a local elementary school.
Jill Scheck, the day camp’s supervisor, told Dateline’s Josh Mankiewicz that Tibbetts was her usual “happy-go-lucky self.”
“She loved being able to play with kids, loved being on the playground, loved being inside doing crafts, loved doing the reading with them,” she said. “That was her cup of tea.”
That day, it was Tibbetts’ turn to close up the camp and she was the last one to leave at around 5:00 p.m. Her brother picked her up and drove her to her boyfriend Dalton Jack’s home, where she was dog sitting while Jack was out of town for work.
Tibbetts texted her mom that she might stop by for dinner later and then got ready for her usual evening run. By the next morning Tibbetts was gone.
Collum, who was exceptionally close to her cousin even though she was seven years older than Tibbetts, remembers she was surprised when Tibbetts never responded to her daily Snapchat message.
“We took great pride in our Snapchat history,” Collum said, adding that she thought the pair had gone at least 600 consecutive days sharing messages with one another.
The staff at the day camp also became concerned when Tibbetts never showed up to work the next day. Scheck reached out to her family, but no one had seen or heard from her.
“I just knew in that moment, this isn’t good,” Collum said, describing being “overwhelmed” by the reality that her cousin was missing.
The college student’s family and friends went to Jack’s home, but the house was empty and there was no sign of Tibbetts, whose wallet and clothes had been left behind.
“We were just so confused and shocked because not a single person had heard from her,” Tibbetts’ best friend Alexis Lynd recalled.
Her family reported her missing to the Poweshiek County Sheriff’s Office at 5:56 p.m., which launched a massive search to find Tibbetts.
"We didn't know if she had a medical issue or if she'd been hit by a car or if she had been abducted,” Poweshiek County Deputy Sheriff Steve Kivi said. “We had no idea.”
Kristina Steward, a hairdresser in Brooklyn, reported seeing Tibbetts running around 7:45 p.m; it was the last time anyone saw her alive.
“She gave a pretty good description of what Mollie was wearing, black running shorts and a pink sports bra. She said that she could see her ponytail bouncing,” said Trent Vileta, the lead agent for the Iowa Department of Criminal Investigation (DCI). “It was our first real definitive time stamp.”
In the days that would follow, hundreds of people showed up to help authorities search the surrounding area — but July in Brooklyn, Iowa, the corn fields are nearly 10 feet high, masking anything inside.
“You could hide 100 bodies along that road and they’d be hard to find,” Vileta said of the significant challenges facing the search teams.
Investigators also took a look at those close to Mollie, but her final text messages didn’t reveal any conflicts with anyone she knew. Jack’s construction coworkers confirmed that, the night she disappeared, he had been hours away at a hotel with the rest of the construction crew.
The FBI analyzed data from Mollie’s cell phone and discovered that from 8:15 p.m. to 8:28 p.m. Tibbetts had been moving at about a 10-minute mile pace before she abruptly stopped for up to four minutes. When she began moving again, she was moving at a 60-mile per hour pace.
“We knew she can’t run that fast, so we knew it had to be in a vehicle,” Vileta said.
Her phone signal died at 8:53 p.m. about 15 miles outside of Brooklyn; Vileta said the phone must have been either shut off or destroyed.
Investigators knew Tibbetts had likely gotten into a vehicle, but where she had gone from there remained a mystery. Someone reported seeing her at a rest stop in Missouri, while another tip suggested she had been in Colorado eating tacos.
None of the leads panned out until investigators went back to the day that Tibbetts disappeared and gathered all the possible video surveillance footage from businesses and homes in Brooklyn along her normal route, to try to retrace her steps.
It was in that surveillance footage that investigators discovered something chilling: A black Chevy Malibu had been circling Tibbetts that night.
They saw Tibbetts — who looked almost like a small dot in the footage — run by a Brooklyn intersection around 7:48 p.m.; the Malibu is spotted for the first time one minute later. In the 20 minutes that followed, the car was seen driving by her two more times.
The footage didn’t capture the car’s license plate number, but the vehicle was unique because of what Vileta described as some “aftermarket stuff” on the car that made it distinctive.
Even with the distinct features on the car, investigators knew it would be difficult to track the vehicle down. But they got the break they needed when Deputy Kivi was driving home on the evening of Aug. 16, 2018 and spotted a vehicle matching the car’s description along the highway.
Kivi quickly called in the plates and began to follow the vehicle at a distance. When the driver stopped and got out, Kivi approached the man, but the driver — later identified as Cristhian Bahena Rivera — didn’t speak any English.
With the help of a nearby neighbor who helped translate, Kivi learned that Bahena Rivera was an undocumented immigrant who was living under an assumed name and working at a local dairy farm.
While he admitted that he was aware that Tibbetts was missing, he insisted that he had nothing to do with her disappearance.
“He seemed cooperative and kind of nonchalant about the whole thing,” Kivi recalled.
Investigators brought him in for questioning four days later. They thought he might open up more to a female officer, but the woman also needed to speak Spanish, so they arranged for a Pamela Romero, an Iowa City Police officer, to conduct the interview.
Romero was not a detective and had never investigated a murder before, but she was quickly able to develop a rapport with Bahena Rivera, a divorced father of a 3-year-old daughter.
“We were joking around, I was asking him about his family, he was telling me everything,” she said in “Dateline: The Last Day.”
Romero was so successful at getting Bahena Rivera to open up that investigators decided she should be the only person in the interrogation room with him.
“We decided to pull her partner out of there because he was only engaged with her,” Vileta said, adding that Bahena Rivera had seemed “almost irritated” that the male investigator had been in the room.
During the interrogation, Bahena Rivera said that he was the only person who ever drove his distinctive Chevy Malibu and admitted to seeing Tibbetts — who he said he had been attracted to — along her running route. But, he initially continued to insist he hadn’t done anything to the missing college student.
“Yes, you have something and you know it,” Romero told him in the interview, “but you’re scared because you know it’ll change your life.”
Romero finally got him to crack and admit to attacking Tibbetts while she was out for her run.
“So he said he saw her, Mollie smiles at him and then he decides to park his car like 100 feet behind her,” Romero recalled. “She was listening to music, so she was not aware that he was behind her.”
He admitted to “fighting with her” and said “she had blood” but told Romero he couldn’t say whether she had been alive or dead when he left her in a corn field.
Bahena Rivera led investigators on Aug. 21, 2018 to the site he'd left her; Tibbetts remains were discovered there, hidden deep within the corn field.
“I fell to the floor and I was just sobbing because you know, I knew in that moment I was never going to get to hug her again and I wasn’t going to welcome her back,” Collum said of the moment she learned her cousin was dead.
Today, Collum runs in honor of her slain cousin.
“We can carry on in Mollie’s legacy in such beautiful ways and pay tribute to the life she lived here on earth,” she said.
"Dateline: Last Day" is available to stream on Peacock.
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