NEW YORK (AP) — A gunman who killed four people inside a Manhattan office tower attributed his mental health issues to the National Football League and intended to attack the league’s headquarters upstairs but mistakenly took the wrong elevator, officials reported on Tuesday.

Investigators disclosed that Shane Tamura, a Las Vegas casino worker, had a handwritten note in his wallet alleging he suffered from chronic traumatic encephalopathy, known as CTE, and accused the league of concealing the risks of brain injuries linked to contact sports.

Tamura, 27, opened fire on several individuals in the skyscraper’s lobby and another on the 33rd-floor office on Monday before taking his own life, according to authorities. Among the victims were an off-duty New York City police officer and a security guard.

The assailant’s grievances with the NFL came to light as police began to reconstruct the events of his life and the cross-country journey that led him to Manhattan. It remains unclear if Tamura exhibited symptoms of CTE, which can only be diagnosed through a post-mortem brain examination.

Tamura, who played high school football in California a decade ago but never reached the NFL, was known to have a history of mental illness, police stated. The three-page note found on his body accused the NFL of hiding the threats to players’ brains for profit. The degenerative brain disease has been associated with concussions and other repeated head trauma prevalent in contact sports like football.

In his note, Tamura repeatedly expressed remorse and requested his brain be examined for CTE. He referenced a PBS Frontline documentary about the disease and cited former NFL player Terry Long, who was diagnosed with CTE and whose suicide in 2005 was noted in the letter.

The NFL long denied the link between football and CTE, but it acknowledged the connection in 2016 testimony before Congress and has paid more than $1.4 billion to retired players to settle concussion-related claims.

The shooting shakes Manhattan

NFL Commissioner Roger Goodell, who works out of the offices, called the shooting “an unspeakable act of violence in our building,” saying he was deeply grateful to the law enforcement officers who responded and to the one who gave his life to protect others.

Goodell said in a memo to staff that a league employee was seriously injured in the attack and was hospitalized in stable condition.

The shooting happened along Park Avenue, one the nation’s most recognized streets, and just blocks from Grand Central Terminal and Rockefeller Center. It’s also less than a 15-minute walk from where UnitedHealthcare CEO Brian Thompson was shot and killed last December by a man who prosecutors say was angry over corporate greed.

The attack drew a response from the White House, with President Donald Trump posting on social media, “My heart is with the families of the four people who were killed, including the NYPD Officer, who made the ultimate sacrifice.”

Video showed the gunman stroll into the building

Tamura, who worked security at the Horseshoe Las Vegas but failed to show up to his shift Sunday, drove across the country over the past few days and into New York City just before the attack, Police Commissioner Jessica Tisch said.

Detectives plan to question a man who supplied parts for the AR-15-style rifle Tamura used Monday, including the weapon’s lower receiver, she said during a news conference.

Nexstar’s reports that Tamura had a work card through the Nevada Private Investigator’s Licensing Board, which expired in December 2024. He also had a permit to carry a concealed weapon. A photo identification of that permit was reportedly found in his possessions.

The Las Vegas Metropolitan police spent several hours Monday evening outside of Tamura’s home. Voting records show he and an older woman live at the address, according to .

A Las Vegas police source told that Tamura was not on their radar but may have had interactions with officers or crisis teams. On Sept. 27, 2023, Tamura refused to leave the Red Rock Casino Resort & Spa in Las Vegas, leading to his arrest, but the charges were later dropped.

In May 2024, Las Vegas police ticketed Tamura for driving without a valid license and registration, documents said. The officer stopped him east of the Las Vegas Strip driving a black BMW sedan, similar to the one involved in Monday’s shooting.

Surveillance video showed Tamura getting out of a BMW early Monday evening and strolling across a plaza in a button-down shirt and jacket with the rifle at his side before he entered the building, which also has offices for the investment firm Blackstone and other companies. It was closed Tuesday except to investigators.

Once inside, he sprayed the lobby with gunfire, killing Didarul Islam, the off-duty police officer who was working a corporate security detail, and hitting a woman who tried to take cover, Tisch said. He then made his way to the elevator bank, shooting a guard at a security desk and another man in the lobby, she said.

“He appeared to have first walked past the officer and then he turned to his right, and saw him and discharged several rounds,” Adams said in a TV interview.

Tamura took an elevator to the 33rd-floor offices of the company that owns the building, Rudin Management, and shot and killed someone there before fatally shooting himself, the commissioner said. He shot himself in the chest, according to Adams.

Blackstone confirmed that one of its employees, real estate executive Wesley LePatner, was among those killed. Security officer Aland Etienne also died, according to a labor union.

The off-duty officer was from Bangladesh

Islam, 36, had served as a police officer in New York City for three-and-a-half years and was an immigrant from Bangladesh, Tisch said. He was working a department-approved second job, in his New York Police Department uniform, providing security Monday at the Park Avenue building.

His body was draped in the NYPD flag as it was moved from the hospital to an ambulance, with fellow officers standing at attention.

Islam leaves behind a pregnant wife and two children. Friends and family stopped by their Bronx home on Tuesday to drop off food and pay their respects.

“He was a very friendly guy and a hardworking guy,” said Tanjim Talukdar, who knew him best from Friday prayers. “Whenever I see him or he sees me, he says ’How are you, my brother?”

The Associated Press contributed to this report.