SUNNY ISLES BEACH, Fla. » The words came up on Alicia Duerson’s cell phone as blithely as text messages typically do, but this one was different: Her ex-husband, former Chicago Bears star Dave Duerson, instructed her to donate his brain for research.

She texted back and heard nothing, then called their son, Tregg, who was just ending his workday as a bank analyst in Chicago. They kept calling and got only voicemail.

The next and last message they received from Dave Duerson was meant for them, their family and perhaps all of professional football. It was written in his hurried hand, repeating his text message in case it hadn’t been received, and found in the South Florida condominium where he placed a gun to his chest and shot himself to death Thursday:

“PLEASE, SEE THAT MY BRAIN IS GIVEN TO THE NFL’S BRAIN BANK.”

Which Dave Duerson wrote that note, and what did it mean? The graduate of Notre Dame or the former Bears safety who, at 50, was finding it hard to remember names and put words together? The father of four, acting charitably, or the football players’ union official all too familiar with retired players dealing with physical decline and dementia? Was it the kid who adored the sport he played growing up in Muncie, Ind., or a man with pointed second thoughts to share?

Alicia and Tregg Duerson can’t know and don’t care to guess. What they do know is that what has stunned the football community — Dave Duerson’s choosing to shoot himself in the chest to preserve his brain for examination — gives them some solace in a sad and confusing time.

“I think it’s just an example of the type of person he is,” Alicia Duerson said. “In his time, he put the future in front of him — future generations of football players in front of him. I’m just so proud of him at this moment.”

Sitting with his mother on the deck of his father’s building Monday night, Tregg Duerson sobbed.

“He was looking for an answer,” Tregg said. “And he was hoping to be a part of an answer.”

The pertinent question is whether Duerson had chronic traumatic encephalopathy, the degenerative brain disease recently found posthumously in about 20 retired players, a disease that has been linked to depression, cognitive impairment and occasionally suicide. That determination will be conducted over the next several months by doctors at the Boston University Center for the Study of Traumatic Encephalopathy, who recently began receiving financial support from the NFL.

The broader issue, given the growing number of football players developing dementia or other cognitive decline, is what the cost of football will eventually be for generations of retired players, and how the game might be made safer for active players, from professionals to peewees.

Duerson’s typed and handwritten final letter, consisting mostly of personal comments that relatives declined to make public, did describe blurred vision and pain, Alicia Duerson said, “on the left side of his brain.” The implication, by pledging his brain to research, was that his problem, and perhaps his suicide as well, stemmed from his football career.

“I would have to guess it was a statement about football and its impact on the brain,” said Robert Smith, a former NFL running back, who served with Duerson on the panel that considers former players’ disability claims. “It had to be. And, his belief that it contributed to his final despair.”

A hard-hitting but nimble defensive back, Duerson was a two-time all-American at Notre Dame and a two-time Super Bowl champion, first as part of the 1985 Bears’ famed 46 defense, then five years later with the New York Giants. He met Alicia during his freshman year at Notre Dame; they divorced last year.

“He was hitting so strong and hard, and he was so aggressive as a defensive back that after the game I was really afraid to go up to him,” she said of their first meeting, after a Notre Dame football game. “He was like: ‘What’s wrong with you? Come over here, let me give you a hug.’ He was so sweet and kind. He could leave the game on the field and go back to being Dave.”

When Duerson left the field for good after the 1993 season with the Arizona Cardinals, he was succeeding in the food service business. He also stayed active in players’ union affairs.

Duerson eventually joined the six-man volunteer panel that considered retired players’ claims under the NFL’s disability plan, then the 88 Plan, a fund that has assisted more than 150 families caring for retired players with dementia since its inception in 2007. Duerson read applications, testimonies and detailed doctors’ reports for hundreds of players with injuries everywhere, including the brain, to the point of institutionalization. He had to vote on whether these people received financial assistance.

In 2007, two congressional committees held hearings into whether the disability board was unfairly denying benefits. Duerson testified before the Senate Commerce Committee alongside Brent Boyd, a former Minnesota Vikings lineman whose depression and cognitive impairment had been ruled unrelated to his playing career, therefore warranting significantly lower benefits. It is unknown how Duerson voted on Boyd’s case. He did get into a testy exchange when Boyd, then 50, asserted that his condition — and that of other players with dementia — was caused by football.

“In regards to the issue of Alzheimer’s, my father’s 84, and, as I had mentioned earlier, Senator, spent 30 years at General Motors,” Duerson said, according to the hearing transcript. “He also has — he also has Alzheimer’s and brain damage, but never played a professional sport. So, the challenge, you know, in terms of where the damage comes from, is a fair question.”

Around this time, Duerson’s life began changing course. His company, Duerson Foods, was forced into receivership. His 17-room home in Highland Park, Ill. — the one with “NFL22” carved on a driveway pillar — went into foreclosure. He pleaded guilty to a misdemeanor domestic battery charge after pushing Alicia during an argument, leading him to resign from Notre Dame’s board. Duerson filed for personal bankruptcy in September.

Few close to Duerson appear to have noticed anything wrong with him. Miki-Yaras Davis, the union’s director of player benefits, said that at a disability board meeting in November, he was his usual joyous, cigar-smoking self. Other union officials said they did not see any signs of cognitive impairment, although one, who spoke on condition of anonymity, said that Duerson once spoke plaintively that he might someday develop chronic traumatic encephalopathy.

Alicia Duerson, who kept in good touch with him, said that he developed a hesitancy in putting words together on paper and in conversation. He also had short-term memory loss that, she said, “got worse as time went on. I think David knew that inside of him there was something wrong.”

Duerson asked that his brain go to the NFL brain bank, an indication that he recognized the league’s support of the Boston University research. After denying and discrediting evidence of football’s long-term impact on the brain for several years, the NFL has increased its efforts to make the game less dangerous through concussion-treatment protocols and rule changes.

“It is a tragic situation that has everyone in the football community feeling both saddened and concerned,” the NFL spokesman, Greg Aiello, wrote Tuesday in an e-mail. “Dave Duerson was a leader, a doer and a giver. He made great contributions to the NFL and to many others. The human tragedy is gut-wrenching, and Dave’s family and friends have been in our thoughts. On the medical side, we will stay in close contact with our medical advisers and the BU research group to understand the facts and their significance.”

Smith said that after joining the disability board last year, he never sensed skepticism from Duerson that players’ cognitive problems were related to football. He acknowledged that Duerson’s personal and financial problems must have contributed to his final act, and that his brain might in fact not show the protein deposits and damaged neurons indicative of CTE.

“He devoted so much to retired players and their problems,” Smith said, “you wish that the information that he had received from all those other cases would have led him to seek the help that could have saved him. That’s what I will have to deal with as my time on the board continues — to do what I can to help get his message across.”

Alicia said that some of Duerson’s ashes, per his longtime wishes, would be spread at Notre Dame and Soldier Field, sites of his finest days. A public memorial service is scheduled for Saturday in Chicago.

Tregg Duerson also played football at Notre Dame, until he decided after one year to concentrate on earning his management degree.

“I just wish he had played baseball,” Tregg blurted angrily at one point during the interview.

But a few minutes later, asked if his father might have had the same second thoughts, he broke into a knowing smile and actually laughed.

“My dad’s not a second-guess type of guy,” he said. “If he makes up his mind, it’s on, baby. There’s no looking back.”