Erie County Coroner Lyell Cook says 51-year-old Larry Cooper, of Philadelphia, was found unresponsive in his cell about 5:30 p.m. Sunday at the State Correctional Institution-Albion.
Cook says Tuesday he has ruled the death a suicide.
State corrections officials say Cooper was serving a sentence of 22½ to 45 years and had been in the prison system since July 1981. Cooper had been moved to prison in Albion, about 25 miles southwest of Erie, in September 2010.
Cooper was serving time for an unspecified conspiracy conviction.
Prison officials treated him in the infirmary then transferred him to UPMC Hamot in Erie where he was pronounced dead Sunday night.