BOSTON — Aaron Hernandez’s death was ruled a suicide on Thursday by Massachusetts officials, who also said that his brain would be released to an academic center that has researched the links between brain disease and football.

The ruling appeared to end a surreal standoff that arose a day after the death of Hernandez, the former New England Patriots tight end who was serving a life sentence for a 2013 murder. Jose Baez, a lawyer who had represented Hernandez, called a news conference on Thursday in front of the Office of the Chief Medical Examiner and accused the state of “illegally” withholding Hernandez’s brain.

By donating Hernandez’s brain, his family could be seeking to find if he had chronic traumatic encephalopathy, or C.T.E., a degenerative brain disease linked to repeated head trauma that has been found in about 100 former N.F.L. players. If Hernandez is found to have had the disease, the diagnosis could be used to help apply for money from a class-action settlement between the N.F.L. and former retired players, or in other legal proceedings.

Symptoms of C.T.E. include memory loss, impaired judgment, aggression, depression and suicidal tendencies.