The posthumous brain examination of Phillip Adams, a 32-year-old retired journeyman N.F.L. player who shot and killed six people in April, revealed that he had an “unusually severe” form of C.T.E., a degenerative brain disease found in athletes and others with a history of repeated hits to the head.

Dr. Anne McKie, director of the C.T.E. Center at Boston University, said an examination of Adams’s brain showed Stage 2 chronic traumatic encephalopathy, an abnormally severe diagnosis for a person in his 30s. McKie added that Adams’s pathology, where significant density was found in both frontal lobes, most nearly resembled that of Aaron Hernandez, a former New England Patriots tight end who was 27 when he died by suicide after being convicted of a 2015 murder.

Adams killed six people in Rock Hill, S.C., his hometown, before barricading himself in his family home and fatally shooting himself. The victims included Robert Lesslie, a prominent local physician; his wife, Barbara; and two of their grandchildren, Adah, 9, and Noah, 5. Adams also killed two air-conditioning technicians, James Lewis and Robert Shook, whom he confronted at the Lesslies’ house.

The police in York County, S.C., said on Tuesday that their investigation had not yielded any connection between Adams and the Lesslies, and there was no documentation showing that Adams was the doctor’s patient.

Lawyers representing Shook’s family requested the findings of the C.T.E. examination as part of a wrongful-death suit against Adams’s estate filed in July. A hearing in the case is set for Jan. 4.

C.T.E., or chronic traumatic encephalopathy, is believed to be caused by repeated blows to the head and can be diagnosed only after death. The degenerative brain disease is linked to alarming symptoms like personality changes, memory loss and impulsive outbursts that may become more pronounced over time.

In a news conference on Tuesday, McKie said the presence of C.T.E., along with social factors, may have contributed to Adams’s behavior.

“Severe frontal lobe pathology might have contributed to Adams’s behavioral abnormalities, in addition to physical, psychiatric and psychosocial factors,” she said. “Theoretically, the combination of poor impulse control, paranoia, poor decision-making, emotional volatility, rage and violent tendencies caused by frontal lobe damage could converge to lower an individual’s threshold for homicidal acts — yet such behaviors are usually multifactorial.”

Adams, a defensive back, was drafted by the San Francisco 49ers in the seventh round of the N.F.L. draft in 2010. He bounced around, playing for the Patriots, the Seattle Seahawks, the Oakland Raiders, the Jets and the Atlanta Falcons before his career ended in 2015.

Adams found it difficult to confront the end of his playing days, those close to him said after the mass shooting. Coming from a town of 65,000 that had produced so many football players it is nicknamed Football City U.S.A., Adams struggled to stay in the league. His last-ditch chance to make an N.F.L. team fizzled.

His behavior had been increasingly erratic ahead of the shooting, according to the friends and associates who knew him best. He remained close to home, caring for his mother, Phyllis, a former high school teacher who became a paraplegic after a car accident a decade ago.

“We cannot say that we are surprised by these results, however, it is shocking to hear how severe his condition was,” an Adams family said in a statement. “After going through medical records from his football career, we do know that he was desperately seeking help from the N.F.L. but was denied all claims due to his inability to remember things and to handle seemingly simple tasks such as traveling hours away to see doctors and going through extensive evaluations.”

Adams’s family agreed to send his brain to be tested for C.T.E. at Boston University, the leading site for research on the disease. According to McKie, over 315 former N.F.L. players have been posthumously diagnosed with C.T.E., including 24 players who died in their 20s and 30s. Most of the younger cohort had Stage 2.

While the results of Adams’s examination provided some questions, others are likely to remain unexplained.