ATLANTA -- Pro wrestler Chris Benoit suffered brain damage from his years in the ring that could help explain why he killed his wife, son and himself, a doctor who studied Benoit's brain said Wednesday.
"These extreme changes throughout Chris Benoit's brain are enough to explain aberrant behavior, including suicide and even homicide," said Julian Bailes, chairman of neurosurgery at West Virginia University and a founding member of the Sports Legacy Institute.
The analysis by doctors affiliated with the Sports Legacy Institute suggests repeated concussions could have contributed to the killings at Benoit's suburban Atlanta home.
The wrestler's father, Michael Benoit, told reporters Wednesday that he knows his son had concussions because his son told him so. But he also said he knows of no medical records or records kept by World Wrestling Entertainment to support the diagnosis.
Steroid use also has lingered as a theory, since anabolic steroids were found in the home and tests conducted by authorities showed Benoit had roughly 10 times the normal level of testosterone in his system when he died.
The institute, which researches the long-term effects of concussions, coordinated the testing using samples of Benoit's brain tissue provided by the Georgia Bureau of Investigation.
"I can't tell you if trauma was the sole or only factor, but these pathological issues are there," said Dr. Robert Cantu, chief of neurosurgery at Emerson Hospital in Concord, Mass. and another founding member of the Sports Legacy Institute. The level of brain damage Benoit had can cause cognitive impairment, dementia, depression and irrational behavior, according to Cantu.
Benoit's brain showed the same degenerative processes that doctors working for the institute found in the brains of four men who had played pro football and committed suicide, but to a worse extent. Head trauma can cause substances called tau proteins to build up in the brain, which in turn can trigger a toxic release of phosphorous, killing brain and nerve cells. Tangles throughout Benoit's brain were telltale signals to doctors that he suffered from abnormal and dangerous tau protein deposits.
Their post-mortem diagnosis: Chronic Traumatic Encephalopathy (CTE), a form of brain damage that is associated with blows to the head and was found in former NFLers Mike Webster, Terry Long, Andre Waters and Justin Strzelczyk.
Indeed, by the time the 40-year-old Benoit killed himself, he had the brain of a man aged 80 or older with "very severe" Alzheimer's disease, according to Cantu. "His was the most extensively damaged of the brains we have examined so far," Cantu said.
There's no evidence that steroid use causes such protein deposits, doctors said on Wednesday, though the issue has not been exhaustively studied. "Are massive doses of steroids good? No. But there is no evidence presently that streroids cause brain cells to die," Bailes said.
With specific reference to Benoit, Bailes added, "In our opinion, brain injury is the only objective finding we can note on the autopsy finding."
The Waltham, Mass.-based institute was founded by former pro wrestler Christopher Nowinski, who has said he had to quit the ring after a kick to the head. Nowinski is president of the institute. He and colleagues have not yet presented their findings to Stamford, Conn.-based WWE, to which Nowinski still has ties.
Cary Ichter, a lawyer for the Benoit family, said his clients haven't decided yet if they will pursue legal action against WWE. A lawyer for WWE did not immediately return a call Wednesday seeking comment. The company has maintained steroid use did not cause Benoit to snap.
Investigators allowed the institute to test Benoit's brain tissue with the permission of his father, Michael Benoit, who lives near Edmonton in Ardrossan, Alberta.
At first, researchers feared Benoit's brain might be too damaged to examine. A source told ESPN.com in June that it was virtually "liquefied" by the time police found Benoit's body. But the condition of the brain was adequate for scientists to "study it with authenticity," according to Cantu.
Michael Benoit said Wednesday that he agreed to the testing because murder-suicide was out of character for his son. Chris Sperry, head of the Georgia Bureau of Investigation, encouraged Benoit to work with Nowinski and his fellow researchers, Benoit said. He also disclosed that after the killings, he discovered a diary written by his son that showed his son was having problems.
"After reading the diary, I would have thought it was written by someone who was extremely disturbed at the time," Michael Benoit said.
Michael Benoit said one neighbor told him that Chris Benoit had walked around his property during the months before the murder-suicide wearing a rosary around his neck. "That would have been completely out of character," Michael Benoit said. "He wasn't religious."
"I think it's the extreme that is in the wrestling industry today," he told reporters. "The human skull is not built to get hit by a chair or something."
Nowinski said concussions can happen in pro wrestling even though many of the moves are staged.
"I got four concussions in three years as a professional wrestler," said Nowinski, who works for the WWE on its initiative to encourage young people to vote. "A lot of concussions happen from mistakes."
Prosecutors have said Benoit strangled his wife with a cord, used a choke hold to strangle his 7-year-old son, placed Bibles next to the bodies and hanged himself on a piece of exercise equipment the weekend of June 22.
Authorities have said Benoit's personal doctor, Phil Astin, prescribed a 10-month supply of anabolic steroids to Benoit every three to four weeks between May 2006 and May 2007. Astin has pleaded not guilty to federal charges of improperly prescribing painkillers and other drugs to two patients other than Benoit.
Information from ESPN The Magazine's Peter Keating and The Associated Press is included in this report