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. Yet a posthumous examination of his brain showed he had such a severe form of the degenerative brain disease C.T.E. that the damage was akin to that of players well into their 60s.

It was, a lawyer for his family said, in announcing the findings on Thursday, “the most severe case they had ever seen in someone of Aaron’s age.”

C.T.E., or chronic traumatic encephalopathy, has been found in more than 100 former N.F.L. players, some of whom committed suicide, according to researchers at Boston University.