The man who killed at least four people Monday night in Manhattan, including a New York City police officer, left behind a suicide note linking his mental health issues to head injuries sustained while playing football.

The note said Shane Devon Tamura, 27, suffered from chronic traumatic encephalopathy, according to CNN. Tamura sprayed bullets around a Manhattan office building Monday, killing Didarul Islam, an NYPD officer. Three other people were killed, and one shooting victim was in critical condition as of Tuesday morning; Tamura later killed himself.

CTE is a brain disease that is associated with multiple, repeated blows to the head. It has become a source of concern for NFL players in recent years.

“Terry Long football gave me CTE and it caused me to drink a gallon of antifreeze,” the three-page note found in one of Tamura’s back pockets said. “You can’t go against the NFL, they’ll squash you.”

Long committed suicide in 2005 by drinking antifreeze, He played for the Pittsburgh Steelers and had been diagnosed with CTE.

“Study my brain please I’m sorry Tell Rick I’m sorry for everything,” the note said.

New York City Mayor Eric Adams said that he believed the offices of the NFL, which were in the building Tamura attacked, were the gunman’s target, according to the New York Post.

“It appears as though he was going after the employees of the NFL,” Adams said.

He said, Tamura “mistakenly went up the wrong elevator banks” at the Manhattan building.

“We’re still going through the suicide note to zero on in the exact reason but at this time, it appears as if it’s something attached to his belief he experienced CTE from the NFL,” he explained.

Caleb Clarke played high school football with Tamura in 2015, according to NBC.

“You never would have thought violence was something you’d associate with him,” Clarke said. “Everything he said was a joke.”

Tamura was a star, he said.

“I don’t think he walked around to be like, ‘Oh, I’ll have NFL games one day,'” he said. “I think it was more of everybody just telling him how great he was. He was the fastest kid I’d ever met, full hands-down. And then, after high school, you know, didn’t see from him that much and didn’t hear from him that much, because he wasn’t on the field.”

“The only thing I can really think of is there was a point where it looked like the sky was the limit, and then it wasn’t anymore.”

Shane Tamura had a manifesto.

Apparently, he discussed the CTE he suffered from football and asked for his brain to be studied.

The NFL was located in the building where he attacked.

It was clear that Tamura had no plans of leaving there alive.

As a football Mama, CTE is… pic.twitter.com/PhYsvAzPDC

— Jennifer Coffindaffer (@CoffindafferFBI) July 29, 2025

New York City Police Commissioner Jessica Tisch said Tamura drove across the country from his Las Vegas home, arriving in New York City on Monday afternoon, according to the Las Vegas Review-Journal.

She said he had mental health issues but did not elaborate.

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