Former NFL player Phillip Adams had CTE when he allegedly gunned down 6 people: BU CTE Center

A former NFL player who police said gunned down six people in April had CTE -- a degenerative brain disease caused by repeated head trauma -- at the time of the mass shooting, the Concussion Legacy Foundation said Tuesday, citing neuropathologists at the Boston University CTE Center.

Phillip Adams died from a self-inflicted gunshot wound after he allegedly carried out the mass shooting at a house in his hometown of Rock Hill, South Carolina. The victims included a doctor, his wife, and two grandchildren, ages 9 and 5.

Adams spent 21 years playing tackle football, starting when he was 7 years old, the Concussion Legacy Foundation said. Adams was drafted by San Francisco in the seventh round out of South Carolina State in 2010 and played as a defensive back for five NFL teams in six years.

Adams had stage 2 CTE at the time of his death at the age of 32, the Concussion Legacy Foundation said.

"Most football players diagnosed with CTE in their 30s have stage 2 CTE. Stage 4 is the most severe stage and is usually associated with dementia," the Concussion Legacy Foundation said in a statement. "CTE has been associated with behavioral symptoms like aggression, impulsivity, explosivity, depression, anxiety, paranoia, and suicidal ideation, along with progressive cognitive symptoms."

Adams "had an extraordinary amount of CTE pathology in the frontal lobe," which "is associated with violent, impulsive or explosive behavior, a 'short fuse,' and lack of self-control," said Dr. Ann McKee, director of the BU CTE Center and chief of neuropathology for the VA Boston Healthcare System.

"His CTE pathology might have contributed to his abnormal behaviors, in addition to other physical, psychiatric and psychosocial factors," she said in a statement.

Adams' frontal lobe CTE pathology was similar in severity to Aaron Hernandez's, McKee said. Hernandez, a former star tight end for New England Patriots, died by suicide in 2017 after he was convicted of murder.

The York County Coroner's Office said in April that Adams would be tested for CTE.

Adams' family said in a statement released by the Concussion Legacy Foundation, "We are pleased to have a better understanding of the mental turmoil that Phillip was dealing with during the last moments of his life. We cannot say that we are surprised by these results, however, it is shocking to hear how severe his condition was."

The family said Adams desperately sought help but had trouble remembering things and was unable to "handle seemingly simple tasks such as traveling hours away to see doctors and going through extensive evaluations. We now know that these deficits were most likely caused by the disease."

"We hope to bring awareness to this condition so that players young and old can understand the risks," the family said. "We will continue to advocate for any research that can prevent any other families from having to endure this type of tragedy."

ABC News' Katie Conway contributed to this report.