An inmate died over the weekend at the United States Penitentiary in Lompoc.
Prison officials say staff discovered the inmate unresponsive in his cell at around 4:20 a.m. Sunday.
Life-saving measures were performed but the inmate was pronounced dead by paramedics, officials say.
The FBI is investigating the death. The inmate’s name has not yet been released.
More than 1,200 inmates are housed at the medium-security facility.