Aaron Hernandez listens to testimony during his double murder trial in Suffolk County Superior Court in Boston this past March. (AP Photo/Elise Amendola, Pool, File)
The brain of late New England Patriots tight end Aaron Hernandez showed severe signs of the degenerative brain disease chronic traumatic encephalopathy, his lawyer said Thursday.
In a news conference at his offices, Jose Baez announced that he had filed a federal lawsuit against the Patriots and the National Football League on behalf Hernandez's young daughter.
Hernandez, who was convicted of first-degree murder in the 2013 shooting death of Boston semipro football player Odin Lloyd, was found hanged in his Massachusetts jail cell this past April.
At the time of his death, the lawsuit claims, "Aaron had Stage III CTE usually seen in players with a median death age of 67 years." Hernandez was 27 years old when he died.
CTE, which can only be diagnosed posthumously, can be caused by repeated head trauma and leads to symptoms like violent mood swings, depression and other cognitive difficulties. A recent study found evidence of the disease in 110 of 111 former NFL players whose brains were examined.
Baez claims that the Patriots and the league were negligent and failed to "disclose, treat or protect" Hernandez from so-called "repetitive impact injuries."
When contacted by Fox News, Patriots spokesman Stacey James said he did not anticipate the team would comment on the lawsuit. When reached by email, NFL spokesman Brian McCarthy wrote, "We have not seen the lawsuit and cannot comment."
A star for the University of Florida when it won the 2008 national title, Hernandez dropped to the fourth round of the NFL draft because of trouble in college that included a failed drug test and a bar fight. His name had also come up in an investigation into a shooting.
In three seasons with the Patriots, Hernandez joined Rob Gronkowski to form one of the most potent tight end duos in NFL history. In 2011, his second season, Hernandez caught 79 passes for 910 yards and seven touchdowns to help the team reach the Super Bowl, and he was rewarded with a $40 million contract.
But the Patriots released him in 2013, shortly after he was arrested in the killing of Lloyd, who was dating the sister of Hernandez's fiancee. Hernandez was convicted and sentenced to life in prison; the conviction was voided because he died before his appeals were exhausted, though that decision is itself being appealed.
A week before his suicide, Hernandez was acquitted in the 2012 drive-by shootings of two men in Boston. Prosecutors had argued that Hernandez gunned the two men down after one accidentally spilled a drink on him in a nightclub, and then got a tattoo of a handgun and the words "God Forgives" to commemorate the crime.
The Associated Press contributed to this report.