The gunman who stormed a high-rise building in the heart of New York City on Monday evening reportedly had a grievance with the NFL.

Shane Tamura, who was identified as the man who killed multiple people including an NYPD officer in the rampage at 345 Park Ave in Midtown Manhattan, cited the NFL in a note left near his body on 33rd floor of the building after he died by suicide, the New York Post reported.

The 27-year-old Nevada resident blamed the sport of football for apparent issues with chronic traumatic encephalopathy (CTE), a side effect from repeated hits to the head, the outlet reported, citing law enforcement sources.

Fox News Digital reached out to the NYPD and the NFL for comment.

Tamura was a high school football player at Granada Hills Charter in Granada Hills, California, which is about 25 miles northwest of Los Angeles.

The NFL’s headquarters were located in the same building where Tamura had killed five people and left several others injured. The league’s officers are on the fifth floor.

NYC Police Commissioner Jessica Tisch said Tamura had a history of mental health problems. 

Tisch said that Tamura traveled cross-country, with his vehicle last being seen in Columbia, New Jersey as recently as 4:24 p.m. ET. That wasn’t long before he unleashed a barrage of gunfire at the high-rise building. 

LIVE UPDATES: NYPD OFFICER KILLED, 4 OTHERS DEAD IN MIDTOWN BUILDING HOME TO BLACKSTONE, NFL

NFL Commissioner Roger Goodell sent a message, obtained by Fox News Digital, to all league employees announcing the traumatic event. One NFL employee was “seriously injured.”

“As has been widely reported, a gunman committed an unspeakable act of violence in our building at 345 Park Avenue. One of our employees was seriously injured in this attack,” the message read. “He is currently in the hospital and in stable condition. NFL staff are at the hospital and we are supporting his family.

“We believe that all of our employees are otherwise safe and accounted for, and the building has nearly been cleared.”

Goodell added to pay attention to all notices with emergency information, as the situation remained fluid.

Fox News’ Scott Thompson contributed to this report.

Follow Fox News Digital’s sports coverage on X and subscribe to the Fox News Sports Huddle newsletter.