The San Diego County Coroner has ruled former longtime NFL linebacker Junior Seau's death a suicide.
Seau, 43, was found dead of a self-inflicted gunshot wound of the chest Wednesday morning at his Oceanside, Calif., home, according to a news release.
His body will be released to the family's mortuary after "completion of administrative responsibilities in the death certificate."
Officials conducted a forensic autopsy, which includes "a full examination of a decedent's body and organs and collection of specimens for laboratory studies."
The Medical Examiner's Office is "awaiting the family's decision regarding study of the brain for repetitive injury by researchers outside of the office," the coroner's release said.
At a press conference outside Seau's home on Wednesday, Oceanside Police Chief Frank McCoy said a woman who identified herself as Seau's girlfriend called 911 at 9:45 a.m. PT and told the dispatcher she had found Seau unconscious in a bedroom with a gunshot wound to the chest.
McCoy said a handgun was found near Seau's body.
Seau played in the NFL for 20 years for the San Diego Chargers, Miami Dolphins and New England Patriots.
His death bears a resemblance to that of other athletes, including Chicago Bears football player Dave Duerson, who shot himself in the chest in February of 2011. Duerson left a note requesting his brain be sent to the "NFL brain bank" for study.
Police did not find a suicide note from Seau, but the former all-star athlete reportedly texted, "I love you," to his ex-wife and three children, and canceled an afternoon photo shoot with the U-T San Diego newspaper, saying he didn't feel well, according to ABC News' Los Angeles affiliate, KABC.
Sports Illustrated reported Thursday that the Boston University's Center for the Study of Traumatic Encephalopathy requested to study Seau's brain, but the magazine later noted that the center attempts to examine the brains of all athletes who die after being involved in hard-hitting sports.
Gina Digravio, a media relations manager with the BU Center, told ABCNews.com that the center has not and will never discuss the details of which brains the researchers are studying or plan to study.
Several former NFL players have committed suicide in recent years, and many experts believe the deaths could be related to repeated blows to the head. In addition to Duerson, ex-Pittsburgh Steelers offensive lineman Terry Long and Philadelphia Eagles defensive back Andre Waters took their own lives.
Chronic traumatic encephalopathy, or CTE, a degenerative and progressive disease found in people who have experienced multiple blows to the head, has shown up in the brains of several former athletes who committed suicide, including Duerson.
The average life expectancy of a retired football player is 58 years, according to the NFL Players Association. That stands in contrast to the average American man's life expectancy of 75 years, according to government data based in 2006.
People close to Seau said the former player suffered several concussions during his career, although he was never listed on any NFL injury report as having a concussion, according to ESPN.
Seau's family tells a different story. When asked whether Seau had experienced any concussions in his career, his ex-wife, Gina Seau said, "Of course he had," according to the Associated Press. "He always bounced back and kept on playing. He's a warrior. That didn't stop him. I don't know what football player hasn't. It's not ballet. It's part of the game."
CTE has similar brain features to that of Alzheimer's, Parkinson's and Lou Gehrig's disease.
The Boston University Center has studied more than 75 brains of dead athletes, and has found CTE in more than 50 of them, according to a January Boston Globe article. CTE was originally researched in 1928 in "punch drunk" boxers, or boxers who suffered from dementia because of continuous blows to the head.
Seau is remembered for his gregarious and positive nature, along with his charity work and involvement in the community. But, that's not to say the 12-time former Pro Bowl player didn't have his share of problems.
In October 2010, Seau was arrested after his live-in girlfriend accused him of domestic violence.
Five hours after posting bail and getting released from jail, he drove his car off the side of a San Diego cliff. He walked away from the accident unscathed, but the police initially investigated the accident as a suicide attempt.
"Exactly how the brain damage causes mood disturbance is not clear," said Dr. John Whyte, director of the Moss Rehabilitation Research Institute in Philadelphia, who does not know Seau's medical history. "There could be biological changes going on, or changes in the neurotransmitters that affect mood, or it could be a psychological factor that this brain injury has disrupted work and family life so much that it has really changed your life."
Repeated blows to the head may also damage parts of the brain that have to do with impulse control and the ability to weigh the long-term consequences of decisions.
Nevertheless, until more research has been done, Whyte said, the public should not jump to conclude a definitive link between the hits Seau experienced and his suicide.
"Some people may feel really bad one day, but they can say, 'OK, this thought is out of proportion with reality,'" said Whyte, "whereas, if you're acting on impulse to certain emotions, you may feel bad one day and that can lead you to take action."
While there has been more concern over pro players and suicide in recent years, Whyte said, sports are likely becoming less dangerous because of all the research being devoted to safety guidelines, proper equipment and the aftermath of a career of brain injuries.
In 2009, the NFL instituted new rules that require clearance from independent neurologists to allow players who suffered concussions to return to the field. The league also imposed stricter guidelines to reduce the number of helmet-to-helmet hits.
"The focus on sports safety has become much more vigilant about brain injuries and more strict with return-to-play guidelines," said Whyte. "But we certainly need more research to confirm whether these athletic-related injuries are leading to suicides."