An employee of the NFL was reportedly "seriously injured" in the mass shooting that occurred at 345 Park Avenue in midtown Manhattan, home to the headquarters for the league. 

The office building, which sits on 52nd Street and Park Avenue, was the site of a tragic mass shooting that left five dead, including one police officer, when a gunman unleashed fire inside before taking his own life. 

NFL Commissioner Roger Goodell sent a message, obtained by Fox News Digital, to all league employees announcing the traumatic event.

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"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. 

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An NYPD officer killed in the shooting has been identified as 36-year-old Didarul Islam, an immigrant from Bangladesh who left behind two sons and a pregnant wife, according to NYPD. He was one of the two uniformed officers at 345 Park Avenue when the shooting occurred, though he was off-duty on Monday working as security for Rudin Management Company inside the building.

"We are deeply grateful to the law enforcement officers who responded to this threat quickly and decisively and to Officer Islam, who gave his life to protect others," Goodell wrote.

NYC Police Commissioner Jessica Tisch identified the shooter, who acted alone, as 27-year-old Shane Tamura, a Las Vegas resident with 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. That wasn’t long before he unleashed a barrage of gunfire at the high-rise building. 

Security video shows Tamura entering the lobby at 345 Park Avenue and immediately opening fire, shooting multiple people. He then shot a security guard behind a desk with an M4 assault rifle, Tisch said. 

Tamura waited for an elevator, where he allowed a woman to leave unharmed before taking it to the 33rd floor. He proceeded to shoot and kill another person before ultimately taking his own life, police said. 

Tamura was licensed to carry a concealed weapon in Nevada.

The NYPD is clearing each floor of the building to make sure everyone was safe, and no other shooters were present. 

As part of his letter to employees, Goodell mentioned the league’s resources that are available to help employees deal with the tragic event. 

"As you know, there are significant resources available to all employees, including grief counselors," Goodell wrote. "Shortly, HR will send you more information on the available resources and how to take advantage of them. 

"Those based in New York should work remotely tomorrow. It is understandable if you prefer to take the day off. There will be increased security presence at 345 Park Avenue in the days and weeks to come. 

Every one of you is a valued member of the NFL family. We will get through this together."

Fox News’ Louis Casiano contributed to this report.

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A lone gunman walked into a midtown Manhattan office building Monday afternoon and opened fire, killing four people – including an NYPD officer – before turning the gun on himself. 

Speaking at a press conference later Monday, NYC Police Commissioner Jessica Tisch identified the shooter as Shane Tamura, a 27-year-old Las Vegas resident with a history of mental health issues. 

Tisch said Tamura had driven across state lines, with his vehicle having been seen as recently as 4:24 p.m. Monday in Columbia, New Jersey, not long before he unleashed a barrage of gunfire. 

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Officers found a rifle case with rounds, a loaded revolver, ammunition and magazines, a backpack, and medication prescribed to Tamura, Tisch said. 

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The vehicle was searched by the NYPD’s bomb squad but found to be clear of any explosives. Police said Tamura is believed to have acted alone and there is no longer a threat to the community. 

"According to our law enforcement partners in Las Vegas, Mr. Tamura, has a documented mental health history," Tisch said. "His motives are still under investigation and we are working to understand why he targeted this particular location." 

The building Tamura entered and opened fire, 345 Park Avenue, is a commercial building where tenants include the NFL, Rudin Management, KPMG and Blackstone. 

Documents obtained by Fox News Digital indicate Tamura had a concealed carry permit that was issued on June 14 and valid for five years. Tamura also carried a private investigator license and had a misdemeanor for trespassing not amounting to burglary in 2023. 

Earlier records show Tamura played football at Granada Hills Charter in Granada Hills, California, which is about 25 miles northwest of Los Angeles. He had also worked as a security guard at a Las Vegas casino per Fox News' Paul Mauro. 

The gunman was armed with a rifle and first opened fire in the lobby of the building on 52nd Street and Park Avenue. He went to another floor and shot people there, sources told Fox News, before going up to the 33rd floor and shooting himself. Police are still searching for a motive in Monday’s deadly shooting.