San Luis Obispo County Jail inmate died from fentanyl use

April 3, 2026

By JOSH FRIEDMAN

The San Luis Obispo County Sheriff’s Office Coroner’s Unit has determined fentanyl to be the primary cause of death for a 48-year-old inmate who died in SLO County Jail last month.

Hypertensive cardiovascular disease also served as a significant contributing condition in the death of Trenidad Castilleja of San Luis Obispo. The coroner’s unit ruled Castilleja’s death as accidental, according to the sheriff’s office.

Shortly before 9 p.m. on March 14, jail staff was dispensing medication to inmates when they recognized Castilleja was in medical distress. Custody and nursing staff immediately attempted to render medical aid and CPR until paramedics arrived.

Castilleja remained unresponsive and was pronounced deceased by paramedics.

San Luis Obispo police officers had arrested Castilleja over three separate cases on Dec. 12, 2024 and booked him in the county jail.

Castilleja had a long history of incarceration with 24 bookings since 1998 on charges including assault with a deadly weapon, forgery, making terrorist threats, burglary and multiple counts of drunk driving.

The sheriff’s office is continuing to investigate the death.

Sheriff’s officials say fentanyl is an extremely potent substance, even in very small amounts. In its pure form, fentanyl is odorless and tasteless, making it difficult to detect and impossible to identify through human senses alone.