LOS ANGELES (CNS) — A state prison inmate serving a life sentence for stabbing an elderly Monrovia couple to death in 2003 has died, and prison officials suspect his cell mate — also a convicted murderer — of killing him, authorities said Sunday.

At approximately 2:05 a.m. Saturday, officials at Kern Valley State Prison in Central California discovered 50-year-old Alfredo Valenzuela, 50, unresponsive in the cell he shared with 36-year-old Noe Herrera during a security check, according to the California Department of Corrections and Rehabilitation.

Staff attempted life-saving measures, and Valenzuela was taken to the institution’s treatment and triage area, however he was pronounced dead at 2:31 a.m.

Officials said Valenzuela’s next-of-kin has been notified.

Herrera was removed from the cell and has been rehoused at the institutions Administrative Segregation Unit pending the homicide investigation.

Valenzuela was sentenced in Los Angeles County in November 2010 to a life-without-parole sentence for two counts of first-degree murder, first-degree burglary and vehicle theft.

Valenzuela murdered Charles “Clark” Shaum, 78, and his wife Bernice Shaum, 70, on either the night of July 25 or the early morning hours of July 26, 2003, after breaking into the couple’s Monrovia home.

In a 2003 interview conducted by detectives, Valenzuela told police he climbed through a window intending to burglarize the couple’s home and landed on top of Bernice Shaum.

He stabbed her more than 40 times, then stabbed her husband 113 times, prosecutors said during the trial.

His attorney argued Valenzuela suffered from brain damage and was on a 10-day methamphetamine binge when he committed the murders.

Valenzuela’s girlfriend, Shawna Lenora Robles, was tried separately and also convicted of first-degree murder for her role in the killings. Prosecutors said she waited outside the bedroom window while Valenzuela stabbed the woman, then was let into the house by her boyfriend and hit Clark Shaum with bolt cutters.

Prosecutors said that after the killings, Valenzuela and Robles stole several items from the home, including a truck.

Herrera was received by the CDCR in August 2019 from Santa Barbara County with a life-with-parole sentence for second-degree murder and attempted second-degree murder.

The Kern County Coroner’s Office will determine the official cause of death.