Doctors say ex-NFL player Phillip Adams had stage two CTE brain injuries when he shot six people dead before turning the gun on himself.

       His case of chronic traumatic encephalopathy, or CTE, was unusually severe, with doctors comparing it to that of Aaron Hernandez, the former player convicted of murder who also died by suicide.

       Adams played in the league for 20 years and, according to his family, was “desperately seeking help from the NFL, but was denied all claims.”

       His family agreed shortly after his death to have his brain tested for CTE, a degenerative disease linked to head trauma and concussions, that has been shown to cause a range of symptoms, including violent mood swings and memory loss. The most severe case of CTE is stage four.

       Ann McKee, a neuropathologist who as director of Boston University CTE Center led the examination of Adams’ brain, presented the findings during a press conference alongside Sabrina Gast, the coroner of York County, where the killings took place.

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       Asked about the connection between CTE and violence, Dr McKee said: “We have seen this behaviour. We have even seen homicidal behaviour in other individuals diagnosed with CTE. It’s difficult to say that it alone resulted in these behaviours because usually, it’s a complicated issue with many other factors.”

       On 7 April, Adams killed Rock Hill, South Carolina physician Robert Lesslie; his wife, Barbara; two of their grandchildren, 9-year-old Adah Lesslie and 5-year-old Noah Lesslie; and two HVAC technicians working at the Lesslie home, James Lewis and Robert Shook, both 38. Police later found Adams with a self-inflicted gunshot wound to the head.

       A toxicology report showed Adams had been using prescription amphetamines, the coroner said. She also noted the presence of Kratum, a drug that can be purchased over the counter, and that in low amounts works as a stimulant and in higher quantities can have an opiate effect. There is no FDA-approved use for the drug.

       CTE, which can only be diagnosed through an autopsy, has been found in former members of the military, football players, boxers, and others who have been subjected to repeated head trauma. One recent study found signs of the debilitating disease in 110 of 111 NFL players whose brains were inspected.

       Adams played in 78 NFL games for six teams over six seasons. He joined the San Francisco 49ers in 2010 as a seventh-round draft pick out of South Carolina State, and though he rarely started, he went on to play for New England, Seattle, Oakland, and the New York Jets before finishing his career with the Atlanta Falcons in 2015.

       His sister said after the killings that his mental health “degraded fast and terribly bad” in recent years and that the family noticed “extremely concerning” signs of mental illness, including an escalating temper and personal hygiene neglect.

       With reporting from the Associated Press