Former New England Patriots TIght End Aaron Hernandez, who was convicted of murder in April 2015 and committed suicide in his jail cell in April of this year, was suffering from a severe case of the degenerative brain disease that has been linked to concussions among former N.F.L. stars in recent years: The brain scan came as a surprise even to researchers who for years have been studying the relationship between brain disease and deaths of professional football players. Aaron Hernandez, the former New England Patriots tight end and a convicted murderer, was 27 when he committed suicide in April.