The lone gunman who carried out a deadly shooting rampage inside a Manhattan office tower that left four people dead before he took his own life reportedly was targeting the offices of the National Football League.

Senior law enforcement officials say that a manifesto and other notes found on 27-year-old Shane Tamura show that the shooter had a fixation with Chronic Traumatic Encephalopathy, writing that the NFL did not do enough to address the head injury common among football players. It is believed that Tamura, whose high school football career was ended by a head injury, had driven cross-country from his Las Vegas home to carry out his attack on the NFL, according to a report from Bloomberg News.

Law enforcement officials told the news outlet that Tamura had picked the wrong elevator bank after storming into the lobby of 345 Park Avenue and had ended up on the 33rd floor, in the offices of real estate developer Rudin Management, instead of the NFL’s office on the fifth floor. The building serves as headquarters for several other major organizations, including accounting firm KPMG and investment company Blackstone.

Surveillance video showed the shooter walking into the prominent 44-story office building in Midtown Manhattan while armed with an M4 rifle. Once in the lobby, Tamura immediately opened fire, striking an NYPD officer.

Didarul Islam, 36, had served with the department for three and a half years and was stationed at the 47th Precinct in the Bronx. On Monday evening, he was working a paid detail assignment in the lobby of 345 Park Avenue when Tamura shot him. Islam, who immigrated from Bangladesh, leaves behind two young sons and a wife expecting their third child, the police commissioner, Jessica Tisch, said during a Monday night press conference.

“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,” Ms. Tisch said.

Tamura then fired at a woman who had sought shelter behind a lobby pillar before unleashing additional gunfire throughout the area.

“He makes his way to the elevator bank, where he shoots a security guard who was taking cover behind the desk,” Ms. Tisch said. Tamura also shot another man inside the lobby during his rampage.

At the elevator bank, Tamura allowed a woman to exit an elevator and walk past him unharmed before heading up to Rudin Management’s offices. Upon leaving the elevator, Tamura continued to fire shots throughout the office, striking and killing a woman.

The gunman walked down the office hallway before turning the rifle on himself and firing directly into his chest. Tamura was pronounced dead at the scene.

During their search of Tamura’s car at the scene, police discovered a rifle case containing ammunition, a loaded revolver, ammunition magazines, and prescription medication belonging to him. A bomb squad inspection of the vehicle found no explosive devices.

According to Ms. Tisch, the shooter departed Las Vegas on July 26 and traveled cross-country, passing through Iowa and Nebraska on July 27. He continued through New Jersey late Monday afternoon before reaching the Park Avenue office building.

The shooting triggered a large-scale police response, with video footage capturing officers rushing to the location as office workers were quickly evacuated from the building.

Images on X showed office employees using office furniture to barricade themselves from the shooter.

Among those struck by gunfire was an employee with the NFL.

In a letter to staffers, the NFL commissioner, Roger Goodell, said that the unidentified employee had been “seriously injured” during the shooting.

“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. He is currently in the hospital and in stable condition,” the commissioner said.

“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,” he added.