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During his playing days, Ewen was a gentle renaissance man when he wasn’t on the ice. He wrote children’s books and crafted models out of hockey tape for his young fans. In 1998, Ewen retired from professional hockey and returned to the St. Louis suburbs to live with his wife, Kelli Ewen. After retiring, Kelli noticed changes in Todd. “We just saw some aggression that we hadn’t previously seen,” she says. “Mood swings, irritability, and not sleeping. Just a pattern of things that was alarming to me.”

Todd’s behavior only became more erratic. During one episode, he choked Kelli and the police had to intervene. In time, depression and reclusiveness replaced Todd’s anger. He routinely became lost and disoriented in the streets around his own home.

Todd confided in Kelli that he feared he might have chronic traumatic encephalopathy, or CTE—a neurodegenerative disease that most experts agree is linked to repetitive head trauma. Research on the disease has largely focused on former professional football players, but it has also been discovered in former NHL players. In 2010, Probert, the Red Wings’ bruiser, became the second NHL player to be diagnosed with CTE. His death was followed in quick succession by the deaths of four other former players, all under the age of 40, all diagnosed with CTE.

In 2013, 10 former players launched a class-action suit against the NHL for their negligence regarding head injuries. Todd was aware of the suit but declined to participate. He ended his life in the basement of his home on the afternoon of September 19, 2015.

Damage to the brain caused by hits to the head has been observed for nearly a century. CTE was originally studied in boxers in the 1920s as dementia pugilistica. In the early 2000s, the Nigerian American neuropathologist Bennet Omalu described the pathology of CTE following research on former professional football players. Since then, CTE has been found in the brains of hundreds of athletes across a wide range of sports. It manifests as small lesions of a protein called tau, which kill the surrounding neurons. The consequences are devastating. Anger, personality changes, and memory loss are common.

After Todd’s death, Kelli and many others were convinced he had CTE. Kelli had Todd’s brain sent to the Canadian Concussion Centre to be analyzed. Six months later, the center’s neuropathologist, Lili-Naz Hazrati, called with shocking results: Todd did not have the disease.

The NHL seized on Hazrati’s negative diagnosis in its defense of the player’s ongoing head-injury class-action suit and in public statements by the league’s commissioner. The NHL’s attorneys argued that Todd Ewen died by suicide because he believed he had CTE, and therefore it would be dangerous for the league to warn players about the disease because they might kill themselves in fear. The NHL contracted 19 expert witnesses, including Hazrati, who in their testimonies injected doubt into the science of CTE. (The NHL did not respond to multiple requests for interviews.)