Advanced stages of CTE found in Aaron Hernandez

— -- BOSTON -- Aaron Hernandez's lawyer says the former New England Patriots tight end's brain showed severe signs of the degenerative brain disease chronic traumatic encephalopathy.

In a news conference at his offices, attorney Jose Baez says testing showed that Hernandez had a severe case of the disease. Baez said the CTE was at Stage 3, with Stage 4 being the highest.

Baez also said a federal lawsuit against the NFL and the New England Patriots on behalf of Hernandez's daughter was filed this afternoon.

CTE can be caused by repeated head trauma and leads to symptoms like violent mood swings, depression and other cognitive difficulties. Hernandez killed himself in April in the jail cell where he was serving a life-without-parole sentence for a 2013 murder. His death came just hours before the Patriots visited the White House to celebrate their latest Super Bowl victory.

CTE can only be diagnosed in an autopsy. A recent study found evidence of the disease in 110 of 111 former NFL players whose brains were examined.

CTE has been linked with repeated concussions and involves brain damage particularly in the frontal region that controls many functions including judgment, emotion, impulse control, social behavior and memory.

A star for the University of Florida when it won the 2008 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 semi-pro football player Odin 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.

Following an investigation into his death, authorities said Hernandez's brain would released to Boston University's Chronic Traumatic Encephalopathy Center, per the request of his family.

BU has studied CTE, a degenerative brain disease linked to football players and other athletes who might have sustained concussions or other head trauma while playing.

Information from The Associated Press was used in this report.