NEW YORK (AP) — A former high school football player, who fatally shot four individuals inside a Manhattan office tower that includes the NFL’s headquarters, was found to have been suffering from CTE, a degenerative brain condition, as stated by New York’s medical examiner on Friday.

According to the New York City medical examiner, Shane Tamura, aged 27, had “clear diagnostic evidence” of early-stage chronic traumatic encephalopathy, known as CTE.

Tamura, a casino worker from Las Vegas who never played professionally in the NFL, perpetrated the mass shooting on July 28. He opened fire in the lobby of a Manhattan building containing the NFL headquarters, which he accused of hiding information about brain injuries.

The victims included a police officer, a security guard, and two employees from companies within the building. An NFL employee was seriously injured but lived through the ordeal.

A three-page note in Tamura’s wallet revealed his belief that he had CTE—a condition only diagnosable posthumously—and requested: “Study my brain.”

His complaints against the NFL included allegations that the league prioritized profits over player safety by concealing the hazards posed by CTE and football.

The brain disease affects regions of the brain involved with regulating behavior and emotions. It has been linked to concussions and other head trauma linked to 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.