A Livermore man was killed in prison while serving a life sentence for the murder of a friend. Authorities say the victim had previously killed for the Aryan Brotherhood.

DELANO – A Bay Area native who allegedly killed the co-founder of a notorious skinhead gang in Orange County was killed in his jail cell, authorities announced Friday.

Jacob Kober, 35, was stabbed multiple times in his cell at Kern Valley State Prison on Thursday, authorities said. His cellmate, 39-year-old Matthew Perez, also suffered injuries consistent with a “prison-made weapon,” according to a news release from the California Department of Corrections and Rehabilitation.

Authorities said only Kober and Perez were in the cell at the time of the murder.

Known as a local methamphetamine and marijuana dealer in the Livermore area in 2015, Kober was serving a life sentence for killing a longtime friend on the fourth hole of a golf course. But in 2018, he was again implicated in murder, this time for a prison stabbing that had repercussions throughout the state's prison system.

The victim was 48-year-old Devlin Stringfellow, an Orange County native and co-founder of the skinhead gang Public Enemy Number One, or PENI. Prosecutors now say his murder was ordered by an Aryan Brotherhood member named William Sylvester, who was convicted of organized crime last April and now faces a life sentence.

Stringfellow's 2018 murder was a typical Aryan Brotherhood attack, according to prosecutors. It happened during a training exercise at California State Prison in Sacramento. Someone hit Stringfellow on the head with a rock to stun him, then Kober and 49-year-old Stephen Dunckhurst allegedly stabbed him, according to testimony at a trial of Sylvester and two other Aryan Brotherhood members.

While awaiting trial, Sylvester reportedly boasted to other co-defendants about ordering Stringfellow's death. Another PENI co-founder, Donald “Popeye” Mazza, later agreed to testify for the government, partly because of his grief over Stringfellow's death, Mazza said during his testimony at the organized crime trial.

Kober was convicted and sentenced to life in prison in 2015 for killing a friend, 28-year-old Kenneth Robert Ogden, in Livermore amid mounting tensions between the two men. Kober had previously accused his girlfriend of having sex with Ogden, and they also had a dispute over money, authorities said at the time. Kober made his money selling drugs and lived just yards from the fourth hole of the Springtown Golf Course, where Ogden's body was found, court records show.

According to authorities, Perez was serving a prison sentence for assault with a firearm and gang activity.

Originally published: September 20, 2024 at 3:25 p.m.