ATLANTA – Pro wrestler Chris Benoit suffered head trauma from his years in the ring that could help explain why he killed his wife, son and himself, a doctor who studied his brain said Wednesday.

The analysis by doctors affiliated with the Sports Legacy Institute suggests that repeated concussions could have contributed to the killings at Benoit’s suburban Atlanta home, though there was no way to know for sure.

“Whether it is the sole factor, I believe, is speculation, and I will not go there,” said Dr. Robert Cantu, member of the Waltham, Mass.-based institute, which researches the long-term effects of concussions.

The level of brain damage Benoit had may have caused depression and irrational behavior, said Cantu.

The wrestler’s father, Michael Benoit, said Wednesday he agreed to the testing of his son’s brain because murder-suicide was so out of character. He said his son complained about concussions, but that he knows of no medical records or records kept by the wrestling league to support the diagnosis.

Steroid use also has lingered as a theory behind the killings, since anabolic steroids were found in Chris Benoit’s home and tests conducted by authorities showed Benoit had about 10 times the normal level of testosterone in his system when he died.

Some experts believe that testosterone use can contribute to paranoia and depression.

Dr. Wendy Wrightsaid multiple concussions could cause long-term brain injuries, but symptoms were unclear.

“This isn’t something you would expect to see turn on one day and have someone fly into a vicious rage,” she said.

Michael Benoit, who lives near Edmonton in Alberta, Canada, said that after the killings, he discovered a diary that he thought “was written by someone who was extremely disturbed.”

He did not elaborate, but he did say a friend told him that prior to the murder-suicide, Chris Benoit had been wearing a rosary, which he said was also out of character.

“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.”

The father said he has not discussed with his attorney whether to take any legal action against World Wrestling Entertainment Inc. or anyone else in the case.

A lawyer for Stamford, Conn.-based WWE did not immediately return a call Wednesday seeking comment. The company has maintained steroid use didn’t cause Benoit to snap.

Richard Decker, an attorney for the mother of Benoit’s slain wife, said the test results “don’t make a lot of difference to us.”

“Even if the theories about the effects of continuing trauma on Chris’ personality are accurate, they don’t rule out Chris’ excessive steroid use, which we know he was involved in, as a factor in the murders,” Decker said. “In either case, it wouldn’t excuse his conduct.”

Associated Press writer Jason Bronis contributed to this report