Investigators said Joe Anthony Rodriguez, 20, was found on his cell floor with severe trauma to his head and body on Wednesday night. He was taken to Community Regional Medical Center where he later died from his injuries.
Detectives said the homicide happened shortly before the nightly inmate count while all of the cell doors where open to the community area of the jail.
Detectives do not know the motive, but said the incident appears to be gang related.
Rodriguez was in custody for the December 2011 murder of 16-year-old Jose Calderon in Southwest Fresno. Authorities are still looking for a second suspect in the murder, 18-year-old Abel Perez.