BAKERSFIELD — Jonathan Hearn pleaded guilty to voluntary manslaughter and other lesser charges Monday in the 2014 killing of a BNSF Railway worker as part of a deal wherein he also agreed to testify against the wife of the slain Helendale man.

Pursuant to the plea deal, Hearn — a former firefighter from Hesperia — will serve up to 25 years, four months in prison, a term to be carried out after the trial for Sabrina Limon, who was arrested late Friday on suspicion of killing her husband, Robert Limon, 38.

Sabrina Limon, 37, was arrested in Camarillo on open charges of murder, attempted murder, solicitation to commit murder, accessory, poisoning and conspiring to commit a crime, authorities said.

Hearn and Sabrina Limon are believed to have been having an affair at the time of Robert Limon's death, Kern County Deputy District Attorney David McKillop has said.

The pair exchanged thousands of text messages, including one in which Hearn suggested he and Sabrina Limon could be together if her husband was out of the picture, according to previous reports.

Robert Limon was shot to death following a work shift at a BNSF industrial complex in Tehachapi in August 2014.

During a two-day preliminary hearing in July 2015, McKillop presented evidence that included still photographs taken from surveillance cameras located at and near the scene of the crime; numerous interviews conducted by detectives; photographs of Sabrina Limon found in a search of Hearn's Hesperia home; several guns also found in the home; and a nylon case found in Hearn's truck filled with ammunition and cash.

Recorded phone conversations between Hearn and Sabrina Limon were also presented. Defense attorney Clayton Campbell previously said the conversations provided only a “compressed view” of “hours and hours” of calls.

Outside the courtroom, Campbell told reporters new evidence involving a prior attempt on Robert Limon’s life recently came to the attention of investigating authorities, who were in attendance Monday.

When asked about specifics, Campbell said he was not at liberty to disclose details; however, Superior Court of Kern County Judge Charles Brehmer referenced a March 2014 date after listing the attempted murder charge.

Campbell said the decision to accept a plea deal was a difficult one for Hearn, who was dressed in a dark-colored suit in court.

“Jonathan … (is) not a cold-hearted, callous, evil man who has no conscience,” Campbell said. “His conscience has compelled him to make this plea bargain. It’s a very difficult decision for anyone to make, to accept that kind of time. But there are several factors that go into it, one of them being his conscience, which I believe is the driving force for him.”

Campbell compared going to trial amid the intense media exposure that has surrounded Hearn since his arrest in November 2014 to “playing Russian roulette when you have three rounds in the cylinder.”

He added that he “expects” Hearn’s testimony will provide crucial evidence to the prosecution’s case against Sabrina Limon.

Prosecutor Eric Smith declined to comment on the ongoing case outside of saying charges will be filed against Sabrina Limon on Tuesday.

In addition to voluntary manslaughter, Hearn also pleaded guilty to attempted murder, poisoning and accessory as part of Monday's plea bargain. He must also offer a formal apology to Robert Limon's family and will be eligible for parole.

Hearn’s family watched from the gallery during Monday’s hearing. They declined a request for comment from the Daily Press following the court proceedings.

A status hearing has been scheduled for April 4 to determine an appropriate sentencing date.

Matthew Cabe can be reached at MCabe@VVDailyPress.com or at 760-951-6254. Follow him on Twitter @DP_MatthewCabe.