A Mule Creek State Prison inmate has admitted to killing his cellmate, pleading guilty last week to first-degree murder in the 2023 slaying. Court records show 42-year-old Alexander Mateuz confessed to killing 23-year-old Robert Aranda and was sentenced to 25 years to life. During the hearing, Aranda’s mother addressed the court with a victim-impact statement.
Amador County District Attorney Todd Riebe said in a news release that Mateuz entered his guilty plea last Thursday, and Amador Superior Court Judge J.S. Hermanson ordered the 25-years-to-life term to run consecutively to Mateuz’s existing California prison sentences, according to The Sacramento Bee. Prosecutors said Mateuz later told others what he had done and credited the DA’s Victim Witness Unit with walking Aranda’s family through the case.
According to the California Department of Corrections and Rehabilitation, the homicide investigation began on Feb. 2, 2023, when staff found Aranda unresponsive in his cell with multiple injuries, including stab wounds. Officers tried life-saving measures and moved him to the prison’s treatment and triage area, where he was pronounced dead roughly 30 minutes later, the agency reported in a news release, per CDCR.
At the time of the attack, prosecutors said Mateuz was already serving a life sentence with the possibility of parole for an August 2008 Los Angeles County conviction and had prior convictions for trafficking drugs into another state prison. Authorities said he was moved into administrative segregation while the homicide investigation unfolded and later admitted to others that he had assaulted Aranda, according to reporting from AOL.
Sentence And Legal Fallout
Judge Hermanson imposed a 25-years-to-life term and ordered it to be served on top of Mateuz’s existing sentences, effectively extending his time behind bars, according to The Sacramento Bee. In the DA’s news release quoted by the paper, Riebe said Mateuz is unable to be rehabilitated and live peaceably in the community and added that he should never be paroled.
Mule Creek's Recent Deaths
Mule Creek State Prison has seen multiple inmate deaths in recent years, including at least two separate cases in 2025 that were investigated as homicides. Officials have highlighted a string of serious incidents at the facility, citing an April 2025 news release and local reporting on a May 2025 case, according to CBS Sacramento.
Prosecutors noted that local district attorneys handle crimes committed within state prisons in their counties, working alongside the California Department of Corrections and Rehabilitation’s Investigative Services Unit. Aranda’s family received ongoing assistance from the DA’s Victim Witness Unit, and court records show that Mateuz remains in state custody. Coverage tied to the DA’s release lists him at Kern Valley State Prison as of the filing, according to AOL.
