A 45-year-old man died in custody early Wednesday morning at the Martinez Detention Facility, Contra Costa County sheriff's officials said.
A correctional deputy conducting room checks at 12:47 a.m. noticed an unresponsive inmate in one of the bunks and called for medical assistance.
Firefighters and an ambulance responded to the scene, but the inmate was pronounced dead. His death appears to be medically related, according to the sheriff's office.
The Contra Costa County District Attorney's Office is investigating the death.
No other information, including the identity of the inmate who died, was immediately released.