THROUGH THE NIGHT and into the next day, as the scrolls across the bottom of television screens spread the news of Derek Boogaard’s death last May, the calls of condolences came, one after another.

Among them was a call from a stranger, first to Joanne Boogaard in Regina, Saskatchewan, then to Len Boogaard in Ottawa. It was a researcher asking for the brain of their son.

An examination of the brain could unlock answers to Boogaard’s life and death. It could save other lives. But there was not much time to make a decision. Boogaard, the N.H.L.’s fiercest fighter, dead of a drug and alcohol overdose at 28, was going to be cremated.

There was little discussion.

The brain was carved out of his skull by a coroner in Minneapolis. It was placed in a plastic bucket and inside a series of plastic bags, then put in a cooler filled with a slurry of icy water. It was driven to the airport and placed in the cargo hold of a plane to Boston.

When it arrived at a laboratory at the Bedford V.A. Medical Center in Bedford, Mass., the brain was vibrantly pink and weighed 1,580 grams, or about 3 ½ pounds. On a stainless-steel table in the basement morgue, Dr. Ann McKee cleaved it in half, front to back, with a large knife. Much of one half was sliced into sheets about the width of sandwich bread.

The pieces of Boogaard’s brain were labeled as SLI-76. They were placed into large, deli-style refrigerators with glass doors, next to dozens of other brains.

The Boogaard family waited for results. One month. Two. Three. Two other N.H.L. enforcers died, reportedly suicides, stoking a debate about the toll of their role in hockey.

Four months. Five. The news came in a conference call to the family in October.

Boogaard had chronic traumatic encephalopathy, commonly known as C.T.E., a close relative of Alzheimer’s disease. It is believed to be caused by repeated blows to the head. It can be diagnosed only posthumously, but scientists say it shows itself in symptoms like memory loss, impulsiveness, mood swings, even addiction.

More than 20 dead former N.F.L. players and many boxers have had C.T.E. diagnosed. It generally hollowed out the final years of their lives into something unrecognizable to loved ones.

And now, the fourth hockey player, of four examined, was found to have had it, too.

But this was different. The others were not in their 20s, not in the prime of their careers.

The scientists on the far end of the conference call told the Boogaard family that they were shocked to see so much damage in someone so young. It appeared to be spreading through his brain. Had Derek Boogaard lived, they said, his condition likely would have worsened into middle-age dementia.

And that was when Len Boogaard’s own mind went numb.

Rehab, Pills and a New Team

The Minnesota Wild prepared for the start of the 2009-10 season. Derek Boogaard watched from a distance.

The team said that Boogaard, the pre-eminent enforcer in the N.H.L. and a hugely popular Wild player, was sitting out a few weeks because of a concussion. Instead, he was at the Canyon treatment center in Malibu, Calif., being treated for addiction to prescription drugs.

Boogaard was embarrassed and worried that news of his addiction would shatter his reputation. He was also concerned that someone would take his role. From rehabilitation, he tracked the preseason fights of teammates and texted friends to gauge how badly he was missed.

He rejoined the team after missing the first five regular-season games and had his first fight on Oct. 21, at home against the Colorado Avalanche’s David Koci. Boogaard started with a left-hand jab to Koci’s chin, then grabbed Koci’s jersey and knocked him down with two right-hand punches.

Boogaard skated, expressionless, to the penalty box.

From the outside, everything seemed normal. It was not.

“His demeanor, his personality, it just left him,” John Scott, a Wild teammate, said. “He didn’t have a personality anymore. He just was kind of — a blank face.”

Boogaard fell asleep while playing cards on the team plane, a teammate said. He passed out in corners of the team’s dressing room. He was uncharacteristically late for meetings and workouts. Wild trainers and doctors warned Boogaard’s teammates not to give him their prescription pills.

Most N.H.L. teams have about 10 affiliated doctors — specialists and dentists with practices of their own. Boogaard had learned that there was no system to track who was prescribing what.

In one three-month stretch of the 2008-9 season with the Wild, Boogaard received at least 11 prescriptions for painkillers from eight doctors — including at least one doctor for a different team, according to records gathered by his father, Len Boogaard. Combined, the prescriptions were for 370 tablets of painkillers containing hydrocodone, typically sold under brand names like Vicodin.

Derek Boogaard increasingly wanted more pills. He became adept at getting them.

In downtown Minneapolis, Boogaard’s favorite hangout was Sneaky Pete’s, a sports bar that becomes a raucous club on weekend nights. Stripper poles are erected on the dance floor, and a throbbing beat escapes beyond the velvet rope out front. Boogaard was a regular.

Young men fueled with alcohol begged Boogaard to punch them, so they could say they survived a shot from the Boogeyman. People bought him drinks. They took pictures of him and with him. They chanted his name. When the attention got overbearing, Boogaard escaped behind the bar, where his bobblehead likeness sat on a shelf.

“He was like Norm in ‘Cheers,’ ” said Stewart Hafiz, whose family owns the bar.

And Boogaard often bought painkillers, thousands of dollars’ worth at a time, from someone he knew there, according to Boogaard’s brother Aaron.

He gobbled the pills by the handful — eight or more OxyContins at a time, multiple people said, at a cost of around $60 each — chewing them to hasten their time-release effect. The line between needing drugs for pain and wanting them for celebration blurred.

“I didn’t trust him to have that amount on him,” said Aaron Boogaard, who lived with Derek in summer off-seasons. “He knew it, too, so he would give them to me to hold, and I would hide them around the place, and he’d come to me when his back was hurt — or whatever was hurting him.”

“What was I going to do?” he added.

Wild coaches saw the decline for a couple of seasons. Boogaard’s admirable work ethic had faded, and no one could pinpoint why.

“I just said to him one day: ‘What’s up? What’s up with you? Where is the guy I know?’ ” said Matt Shaw, who coached Boogaard as an assistant with the minor league Houston Aeros and, later, with the Wild. “Because he was not himself. And he didn’t have an answer. He didn’t want to look me in the eye.”

Boogaard had been drafted by the Wild in 2001, a seventh-round pick given little chance of making the N.H.L. The Wild shepherded him through three seasons in the minor leagues and molded him into the most fearsome player in hockey. They saw how his gentle humility blossomed into fearless swagger. They felt how the game changed when he strode onto the ice.

But by the 2009-10 season, Boogaard was 27, and his body carried a lot of mileage. He missed the start of the season while in rehabilitation, and his contract was to expire at season’s end. He played 57 games, and had no goals and nine fights.

The Wild quietly dangled him as trade bait, then made a half-hearted attempt to re-sign him for about $1 million a year.