How geofencing technology cracked the case of a woman who vanished

By all accounts, Nancy Woodrum was the kind of woman who made everyone around her feel like they mattered.

Woodrum, 62, was the owner of a hair salon in Paso Robles, California, who lived alone in her Victorian-style ranch home, named Paradise Ranch, after her husband Robert died a few years prior.

"Nancy clicked with everybody," Louisa Spadia Beckham, who knew Woodrum from the salon, told "20/20." "She just had that amazing gift of just openness, kindness, just generous."

However, Woodrum's daughter, Amanda Peel, became concerned after getting a phone call on May 5, 2018.

A new "20/20" episode, "The Vanishing of Nancy Woodrum" airing Friday, March 13, at 9 p.m. ET on ABC and streaming the next day on Disney+ and Hulu, examines the case.

You can also get more behind-the-scenes of each week's episode by listening to "20/20: The After Show" weekly series right on your 20/20 podcast feed on Mondays, hosted by "20/20" co-anchor Deborah Roberts.

Woodrum "had not shown up to her Bible study group," Peel said, which was unusual since she was a devout Jehovah's Witness.

"I had her neighbor go over there to check on her," she told "20/20." "She said, 'The door's wide open, the TV's blaring, and you better come over here.'"

Peel went to investigate the home, finding what appeared to be blood spattered in her room and her bedsheets missing.

Investigators began looking for Woodrum, soon finding her missing bedding and clothes discarded on the side of a highway, a few miles away from Paradise Ranch.

Police wondered if someone who knew Nancy could have been responsible for her disappearance and investigated various leads over the next few months --weekend guests staying at the ranch,a contractor, even a member of her own family. But none of those panned outand they were all eventually cleared, and the case languished for more than seven months.

Then police deployed geofencing, a cellphone tracking technology that was new at the time, at Paradise Ranch.

"You can put a fence, a virtual fence around an area, a house, a property, and Google will track which Google accounts, emails or cell phones come within that fence in a given period of time," prosecutor Chris Peuvrelle told "20/20." "In order to obtain Google geofence information, search warrants needed to be written and served upon Google for a very specific time period."

It allowed investigators to identify any devices that entered Woodrum's house on the night of her disappearance. This led them to Carlo Fuentes Flores, who was part of a painting crew that was contracted out for renovations at Paradise Ranch.

Police followed Fuentes Flores and surreptitiously pulled his DNA off a Coke bottle he drank from at a restaurant. They found that it matched DNA found in Woodrum's bedroom on the night she went missing.

Investigators brought Fuentes Flores in for questioning, where he said he would take investigators to Woodrum's body. He led them to a remote area called Carrizo Plain, an hour outside of Paso Robles, where policesaid theyfound her skeletal remains.

In a subsequent interrogation, Fuentes Floresadmitted to sexually assaulting Woodrumat Paradise Ranch, while intoxicated, and suffocating her with her pillow to cover up the assault.

Police arrested Fuentes Flores in December 2018, charging him with Woodrum's murder after he wrote a letter of apology to her family and his.

Peel told "20/20" she felt comforted when her mother's body was located.

"Therewas relief. I just wanted to find her. We needed to have some closure," she said. "There'sa lot of people who never get answers."

Fuentes Flores pleaded not guilty, despite his previous confession, admissions of guilt to his wife in recorded jail calls and apology letter.The defense argued that any previous claims of guilt were forfeit, as there should have been a Spanish translator presentduringthe police interviewwith the Mexican-born Fuentes Flores, as his first language was Spanish.

However, the judge found him guilty of first-degree murder during a rape, sentencing him to life in prison without parole in February 2022.

Fuentes Floreshad taken aslowplea that allowed him to appeal his conviction, but it was denied by the California Court of Appeals in July 2023.

Peeltold "20/20" she still remembers all the love her mother spread throughout her life.

"She was an amazing person. She loved God. She wanted that to befirstin her life. And she wanted people to know that," she said.