Trial: Man Accused Of Fatally Shooting Wife's Former Boyfriend

RIVERSIDE, CA — Prosecution testimony is expected to wrap up this week in the trial of a 35-year-old man accused of gunning down his wife's ex- boyfriend in Jurupa Valley.

Tyler Catlin Borg of Fontana is charged with first-degree murder and sentence-enhancing gun and great bodily injury allegations for the 2018 slaying of 31-year-old Justin Adrian Kiernan of San Bernardino.

The prosecution began calling witnesses at the end of last week and is slated to conclude its case-in-chief by Thursday at the Riverside Hall of Justice.

Borg, who has been in custody since the day after the shooting, is being held without bail at the Robert Presley Jail in Riverside. The defendant, who has no documented prior felony convictions, could face 50 years to life in state prison if convicted.

According to the District Attorney's Office, the defendant and his wife, identified in court documents only as "C.M.," had been experiencing marital trouble for most of their three-year union.

A trial brief filed by the prosecution said that in December 2018, C.M. initiated contact with Kiernan, meeting him at his workplace, the San Manuel Baseball Stadium, on Dec. 15.

The two had not seen each other since she broke off their relationship to wed Borg. The victim and C.M. both expressed an interest in rekindling their romance, and after a few minutes, she drove away, and he returned to work, according to the prosecution.

Borg was suspicious as to his wife's whereabouts that day and confronted her about it when she got home. When C.M. insisted that she had been at a shopping mall, the defendant "told her he knew she was lying to him because he had placed a GPS tracker on her car," the brief alleges. The defendant and his wife argued, but she denied any wrongdoing, and the matter was left unresolved.

"Meanwhile, C.M. and Justin Kiernan continued to exchange text messages," according to the brief. "The messages became sexual in nature. C.M. sent Justin explicit photos of herself. Justin and C.M. lamented on how they should have engaged in sexual activity when they met (days earlier)."

The two discussed possibly arranging a tryst, but on Dec. 22, 2018, Borg took possession of his wife's mobile phone and scrutinized all of her texts until finding the string between her and the victim, according to prosecutors.

The defendant allegedly told his wife that their marriage was over and that he was going to take her to her parents' home in Jurupa Valley. Borg then allegedly began communicating with Kiernan, pretending to be C.M. by using her phone, investigators allege.

The defendant allegedly convinced the victim that C.M. wanted to meet him near her parents' house in the 7800 block of Virtue Vista Drive, near Paisano Way, on the night of Dec. 22.

The prosecution alleges Borg took his wife to the residence and went inside to speak with her parents, telling them the marriage was finished while continuing to text back and forth with Kiernan, pretending to be C.M. No one was aware that Borg had allegedly armed himself with a 9mm semiautomatic pistol, according to the trial brief.

C.M.'s father asked Borg to contact Kiernan and tell him to stop communicating with his wife, but "the defendant maintained his determination to confront Justin that night," according to the brief.

When Kiernan arrived and parked halfway down the street, expecting to meet C.M., he texted her, but Borg received the message and bolted from her parents' home to confront the victim.

The prosecution alleges the defendant ran up to Kiernan's blue Kia sedan and fired five shots, one of which struck the victim in the upper back, and the other in the back of the head, killing him instantly.

Borg allegedly fled in his car and went to his sister's residence in Hemet. Sheriff's detectives went to the Jurupa Valley location spoke with witnesses, quickly identifying Borg as the alleged perpetrator. He was tracked down and taken into custody the following morning.

—City News Service