The gunman who killed four people in a Midtown Manhattan office building on Monday night wanted to shoot up the NFL headquarters, Mayor Eric Adams has confirmed.

Shane Tamura, 27, entered the building that houses NFL headquarters, 345 Park Ave., with the intent to attack the football league’s offices. A former high school football player, Tamura carried with him a three-page note that claimed he suffered from chronic traumatic encephalopathy, a trauma-induced head injury, and expressed that the NFL has hidden the danger of contact sports.

The shooter “mistakenly went up the wrong elevator banks” and ended up on the 33rd floor at the Rudin Management real estate firm, instead of at NFL HQ, Adams said on Tuesday. Tamura shot himself dead on that floor after he opened fire in the Park Avenue high-rise’s lobby, killing four and injuring a fifth.

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

NFL Commissioner Roger Goodell seemed to confirm that the fifth surviving victim was an NFL employee, as he told the league in a letter that an NFL employee had been “seriously injured.”

Tamura gained access to the elevator banks after he killed an off-duty New York Police Department officer who was working at the building’s security desk. Didarul Islam, 36, was a Bangladeshi immigrant and father of two young sons, with a third baby on the way. He was an NYPD officer for three-and-a-half years.

“He put himself in harm’s way, he made the ultimate sacrifice – shot in cold blood, wearing a uniform that stood for the promise that he made to this city. He died as he lived, a hero,” Police Commissioner Jessica Tisch said.

Wesley LePatner, an employee of Blackstone, which also had offices in the building, was among those killed. She was “brilliant, passionate, warm, generous, and deeply respected within our firm and beyond,” the company said in a statement.

Tamura had a Las Vegas address and played high school football in California. Police found a rifle case with ammunition and magazines and a loaded revolver in his vehicle, which traveled cross country through Colorado to New Jersey late last week.