A man who gunned down four people, then killed himself in a Manhattan skyscraper may have targeted the American football league because he blamed it for brain injuries he claimed he suffered, New York mayor Eric Adams said overnight.
Information that the killer carried in a note referring to the degenerative brain disease CTE offered a possible motive for the Tuesday shootings at offices used by the National Football League, among others.
A source confirmed that in a three-page handwritten note found in the gunman's wallet, he wrote: "Chronic traumatic encephalopathy (CTE). Study my brain please. I'm sorry."
"Football gave me CTE and it cause me to drink a gallon of antifreeze. You can't go against the NFL. They'll squash you."
The suspected shooter, identified as 27-year-old Shane Tamura, went on to ask that his brain be studied for CTE, and alleged that the league "knowingly concealed the dangers to our brains to maximise profits".
Armed with a semi-automatic rifle, the attacker shot a police officer outside the tower on Park Avenue, then opened fire in the lobby before trying to access the NFL's offices.
Tamura had never actually played for the top professional league, Adams said, though he was reportedly a star player in high school in California.
The bloodshed sparked a massive police response in the teeming centre of the city — not far from where a man with a grievance against UnitedHealthcare gunned down the medical insurance company's CEO last December.
New York police commissioner Jessica Tisch told a news conference that Tamura had a history of mental health issues.
US President Donald Trump on Tuesday called the mass shooting a "senseless act of violence" carried out by a "lunatic".
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