NEW YORK (AP) — The former high school football player who killed four people inside a Manhattan office tower that houses the headquarters of the NFL, and who blamed the league for hiding the dangers of brain injuries, was suffering from the degenerative brain disease CTE, a city medical examiner said Friday.

Shane Tamura, 27, had “unambiguous diagnostic evidence” of low-stage chronic traumatic encephalopathy, commonly known as CTE, according to a report from the New York City medical examiner.

Tamura, a Las Vegas casino worker, shot himself in the chest after a July 28 mass shooting that killed a police officer, a security guard and two others who worked inside the building.

He had intended to target the NFL office, officials said, but took the wrong elevator. One league employee was wounded in the building’s lobby but survived.

In a three-page note found in his wallet, Tamura said he believed he had CTE — diagnosable only after death — and implored those who found him: “Study my brain.”

Among his grievances against the NFL was a claim that the league put its profits ahead of player safety by concealing the harm CTE, and football, can cause.

Tamura didn’t play professional football but played during his high school years in Southern California, where he grew up.

“There is no justification for the horrific and senseless acts that took place,” the NFL said in a statement. “As the medical examiner notes ‘the science around this condition continues to evolve, and the physical and mental manifestations of CTE remain under study.’”

The disease affects regions of the brain involved with regulating behavior and emotions. It has been linked to concussions and other head trauma associated with contact sports, with evidence of the disease found in both professional and high school athletes.

After more than a decade of denial, the NFL conceded the link between football and CTE in 2016 testimony before Congress, and has so far paid more than $1.4 billion to retired players to settle concussion-related claims.

Tamura had twice been hospitalized during mental health crises in recent years, officials said.

During a 2022 incident, his mother told 911 dispatchers that her son was threatening to kill himself, adding that he suffered from “depression, concussion like sports concussion, chronic migraines, and insomnia.”

The following year, he was arrested on a misdemeanor trespassing charge after becoming agitated when he was told to leave a suburban Las Vegas casino. Prosecutors later dismissed the case.

The medical examiner’s report did not reach a conclusion on the cause of the disease but noted it was often found in those “with a history of repeated exposure to head trauma.”

Dr. Daniel Daneshvar, chief of brain injury rehabilitation and associate professor at Harvard University, said even a low-stage diagnosis of CTE could be responsible for “behavioral changes and impulse control problems,” which often progressed with age.

But he cautioned against drawing a direct line between the disease and a person’s specific actions.

“Pulling the string and figuring out which process is responsible for someone’s actions is not something we’re able to do,” he said.