How investigators solved the love triangle murder case of Sabrina and Robert Limon

SILVER LAKES, Calif. -- In the small community of Silver Lakes, California, Sabrina and Robert Limon were once the life of the party. The so-called "it couple" was known for throwing booze-filled gatherings for their tight-knit group of friends dubbed "the wolf pack."

But when a firefighter named Jonathan Hearn swept Sabrina off her feet, it led to a sordid crime that no one saw coming.

The love triangle murder case involving wiretapping, Bible verses and allegations of poisoned pudding is the subject of a new "20/20" airing April 7 at 9 p.m. ET. The broadcast features interviews from friends, family and investigators, and ABC News' Deborah Roberts goes back to the location of the murder with detectives to retrace the investigation.

In 2008, Sabrina and Robert Limon decided that they wanted to have a bit more excitement in their lives, so they opened up their marriage to other couples.

"They went on adult vacations. They went out boating. They partied a lot at the North Lake," Julie Cordova, Sabrina's sister, told "20/20."

Cordova said that Sabrina eventually grew "tired of being in an open marriage" and "wanted [the couple] to go back to church," but her husband didn't want anything to change.

"Sabrina was drinking so much, all the time, that she was pretty numb," Cordova said.

On Aug. 17, 2014, Robert was shot and killed while working at the BNSF railyard in Tehachapi. Investigators believed the crime scene had been staged to look like Robert was killed during a botched robbery, former Kern County Detective Darin Grantham told "20/20."

But who would have a motive to kill the beloved husband and father of two?

"He was well-liked by everyone and no one could imagine any reason why someone would want to kill Robert," former Kern Country Detective Tommy Robins told "20/20."

Detectives scoured the area for surveillance cameras. Footage from the railyard around the time of the murder showed an unknown man limping around. A nearby company provided surveillance video that showed Robert Limon on the road that led to his office, with multiple other vehicles on the road. All of the other motorists, with the exception of a man on a motorcycle, were able to be identified, Grantham said.

That motorcyclist's identity remained a mystery until investigators received a call two weeks after Limon's death. Jason Bernatene, a friend of the Limons, told detectives that he got a strange voicemail from a man named Jonathan Hearn, who seemed "very apologetic for Rob's death," Grantham said.

The tip put Hearn on detectives' radar for the very first time and changed the course of the investigation.

Detectives would learn that Sabrina and Hearn were having an affair after meeting at a Costco where Sabrina worked part-time. Bonding over their shared Christian faith, they started a relationship behind Robert's back. Eventually, Robert Limon discovered intimate texts between the two on Sabrina's phone and demanded Sabrina end the affair. But she kept seeing Hearn.

In the wake of Robert's murder, detectives decided to wiretap Sabrina and Hearn's phones. The couple talked a lot about God and the Bible. In one exchange with Sabrina, Hearn can be overhead saying, "Hi God. We are on our knees for a reason. We have been dirt bags, we've been sinners. We've been selfish and we sinned."

Despite some intriguing exchanges between the couple, nothing proved a murder plot against Robert, detectives said. Investigators then decided to feed Sabrina false information about the murder investigation to see how she would react - Sabrina immediately called Hearn on a burner phone to alert him about the new details.

On Nov. 18, 2014, Hearn and Sabrina were arrested on suspicion of killing Robert. At Hearn's home, detectives found a motorcycle, a helmet, a red bandana and a backpack matching the description of a mystery man seen on surveillance footage in the area where Robert was killed, and a grocery bag full of receipts, authorities said.

Within a few days, Sabrina was let go from custody due to insufficient evidence linking her to the crime, while Hearn, charged with murder, remained behind bars.

Hearn struck a plea deal that would give him a 25-year sentence in exchange for testifying about Sabrina's alleged involvement in the murder scheme.

Two years after her husband's death, Sabrina was arrested for his murder. She pleaded not guilty to all charges.

At trial, Hearn admitted to killing Robert and alleged Sabrina helped him plan it, after she rejected Hearn's suggestion to divorce her husband. Hearn testified that Sabrina "expressed that [Robert] would honestly rather be dead than divorced...Losing her would essentially kill him." Hearn also claimed there was a first failed plot to poison Robert's banana pudding with arsenic prior to the fatal shooting. Hearn testified that when it came to the fatal attack on Robert in Tehachapi, Sabrina provided a layout of the BNSF facility and Robert's work schedule.

Testifying in her own defense, Sabrina denied any involvement in planning her husband's murder, along with the attempted poisoning plot alleged by Hearn. Richard Terry, Sabrina's defense attorney, argued that Hearn's plea deal gave him an incentive to lie on the stand.

As for the wiretapped conversations, Sabrina Limon said at trial, "[Jonathan] wanted to know everything that was going on, and I told him. I trusted him. He had told me that, you know, just the dangers of what could happen when an affair is exposed, how the police think and how they work."

On Feb. 21, 2018, Sabrina Limon was convicted on four of the six counts against her, including first-degree murder, attempted murder, solicitation of murder and conspiracy. She was acquitted of the alleged poisoning attempt on Robert's life. She was sentenced to 25 years to life in prison.

In January, the California Supreme Court denied a petition to review Sabrina's murder conviction after she previously appealed for a new trial.

Hearn was convicted of manslaughter, not murder, and sentenced to 25 years and four months in prison.