NEW YORK (WPIX) – A note found on the Manhattan gunman who killed four people read that he had suffered a brain injury, according to Mayor Eric Adams.

Adams said that 27-year-old Shane Tamura blamed the NFL for his injury.

“He was not an NFL player,” Adams said. “It appears as though he was blaming the NFL for his CTE… and he shot himself and took his own life. Shot himself in the chest. It appears to have been that he wanted to preserve his brain for reason of research.”

Officials said Tamura shot and killed three people in the building’s lobby, including New York Police Department Officer Didarul Islam, who was working a private detail; another security guard, and Blackstone executive Wesley LePatner. An NFL employee in the lobby was also shot and was hospitalized for his injuries, according to authorities.

Tamura, who intended to head to the NFL offices, then accidentally went into the wrong elevator and headed up to Rudin Management, Adams said.

The security guard, who was shot and killed while ducking for cover behind a desk, would have been able to turn off the elevators to prevent Tamura from going up, according to Adams.

Police said that in the Rudin Management offices, Tamura killed one more person before shooting himself. He died of a self-inflicted gunshot wound, according to authorities.

The gunman did not appear to contact the NFL before the shooting, according to Adams.