This article originally appeaerd on People.

Aaron Hernandez suffered a traumatic brain injury playing football, and his family will file a multimillion-dollar lawsuit against the NFL and the New England Patriots, his attorney tells PEOPLE.

After the 27-year-old committed suicide in prison on April 19 while serving a life sentence for murder, authorities performed an autopsy and released his brain to Boston University’s Chronic Traumatic Encephalopathy Center. Researchers at the university have been studying traumatic brain injuries and their link to football.

Now, attorney Jose Baez tells PEOPLE the results show Hernandez suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease that has been linked to head trauma. The disease has been found in dozens of former NFL players.

In July, Boston University researchers published a study in the Journal of the American Medical Association that claimed that CTE was detected in 99 percent of brains obtained from National Football League players. Some have cautioned that the findings might have a selection bias because the brains were submitted by family members of players who showed possible symptoms of the disease.

 

CTE cannot be diagnosed in living subjects; it is only found during autopsies. Several former NFL players, including Junior Seau, were diagnosed with the disease after committing suicide.

“We got the results back and found that not only did he have CTE, but it was the most severe case that they’ve ever seen in a football player of his age,” Baez tells PEOPLE. “There are four stages of CTE, and Aaron was a stage 3 at age 27.”

Hernandez’s family believes the CTE contributed to some of his behavior. He hanged himself with a bed sheet just five days after he was acquitted of double murder charges in the deaths of two men outside a Boston nightclub in 2012. He was still serving a life sentence for the 2013 murder of Odin Lloyd, his fiancée’s sister’s boyfriend. He was not eligible for parole.

 

“While we still maintain that he was innocent [of the murders], the CTE can explain a lot of his behavior,” Baez says. “The impulsiveness can be a symptom of CTE. We think that the CTE explains a lot of things that Aaron did, including his supposed suicide.”

Symptoms of CTE can include aggression, depression, diminished impulse control, memory loss, impaired cognitive skills and suicidal tendencies.

“There’s no question that the CTE is a result of playing football,” Baez continues. “They need to be held accountable. We are filing a lawsuit against the NFL and the New England Patriots. It’s a loss of consortium claim for his daughter. She’s growing up without a father because of the negligence of the NFL.”

Neither the NFL or the New England Patriots returned PEOPLE’s calls for comment.

With Hernandez’s death, his conviction for Lloyd’s murder was voided because of a little-known legal doctrine in Massachusetts that vacates convictions if a defendant dies before their direct appeal is complete.