The Nevada resident who stormed into a Midtown Manhattan skyscraper wielding an M4 assault rifle, fatally shooting four individuals before taking his own life, might have been motivated by a grudge against the National Football League.

Shane Tamura, 27, was discovered with a letter on him suggesting he harbored resentments towards the NFL and its approach to chronic traumatic encephalopathy (CTE) following the tragic incident at 345 Park Avenue.

In the note he railed against the NFL and pleaded for his brain to be studied.

“Terry Long football gave me CTE, leading me to consume a gallon of antifreeze,” Tamura reportedly wrote, as per CNN. “You can’t stand up to the NFL; they’ll overpower you.”

The shooter was referring to former Pittsburgh Steeler Terry Long, who committed suicide by drinking antifreeze in 2006 after suffering from CTE.

‘Study my brain please I’m sorry Tell Rick I’m sorry for everything,’ the note read. 

Authorities say Tamura traveled all the way from his home in Las Vegas in his black BMW, passing through Colorado on July 26 and making his way through New Jersey to Manhattan. 

He was then caught on chilling surveillance footage wearing a sport coat and button-down shirt while carrying a large assault rifle into the building, which houses the headquarters for the NFL. 

The gunman then opened fire inside the lobby just before 6.30pm.

Tamura had been a star football player in high school, obsessed with the game and once on a path that suggested a future defined by discipline and teamwork.

During his senior year, he even earned six Player of the Game awards and registered 126 carries for 616 rushing yards and five touchdowns in nine appearances.

But in more recent years, Tamura had a ‘documented mental health history,’ NYPD Commissioner Jessica Tisch revealed at a news conference.

Yet Tamura earned a private investigator’s license and was able to obtain a concealed carry permit to carry firearms, both legally granted through the Las Vegas Sheriff’s Department. 

He had the license on him when he marched into the building and opened fire.

Officer Didarul Islam, a 36-year-old father-of-two who was working private security at the time, was then shot in the back and killed and an unidentified security guard who took cover behind a desk was also targeted.

From there, police say Tamura  took the elevator up to the 33rd floor and the offices of Rudin Management, which operates the building, and shot and killed a third victim before taking his own life.

The National Football League headquarters are on the fifth floor of the building, which law enforcement officials say Tamura did not travel to.

However, an employee of the league was ‘seriously injured,’ according to a memo to staff written by NFL Commissioner Roger Goodell and obtained by CNN.

He said the unidentified employee was rushed to the hospital, where other league employees are comforting his family.

All of the other employees are believed to be safe and accounted for, Goodell said, as he vowed to boost security at the league’s headquarters ‘in the days and weeks to come.’

In the meantime, police in New York City and in Nevada are continuing to comb Tamura’s social media presence and are rifling through his Las Vegas home to collect evidence pointing to a motive.

They have already found a rifle case with rounds, a loaded revolver, ammunition and magazines, as well as a backpack and medication prescribed to him inside his vehicle.

It is now believed Tamura was the sole shooter in the broad daylight attack, as police say there is no evidence he had an accomplice.

Still, officers are continuing to work to determine whether anyone may have helped plan or facilitate his movements across state lines or into the high-security office tower, which was put on lockdown as heavily-armed police officers swarmed the floors.

Photos from the scene showed scores of people in business attire frantically leaving with their hands up, as others inside the building barricaded the doors with furniture to prevent Tamura from entering. 

The shooting also led to a chaotic scene in Midtown Manhattan, with nearby worker Anna Smith, who had just stepped out to grab dinner, describing the ‘crowd panic’ that wafted over the area.

‘People just started running,’ she said. ‘We had no idea what was going on.’

Another witness told The New York Post that ‘it sounded like a barrage of shots …Like an automatic weapon. Like a high-capacity weapon.’

Another person told the paper that a ‘guy came in with an assault rifle and started shooting.’ 

A shocking image showed the victim splayed out on the floor of the office building after he suffered the self-inflicted gunshot wound. 

His bloodied weapon, which was equipped with a silencer, was found nearby.

Meanwhile, the city’s emergency management system issued alerts about road closures, subway disruptions, and traffic delays around Grand Central Terminal and St. Patrick’s Cathedral – both just blocks from the shooting scene.

As night fell, many turned their attention to the loss of Officer Islam, who was working in private security for Rudin Management Company Monday night, according to The New York Post. He regularly works in the Bronx’s 47th precinct

‘He was doing what he does best, as all members of the police department carry out he was saving lives,’ New York City Mayor Eric Adams said at an evening news conference.

‘He was protecting New Yorkers. He’s an immigrant from Bangladesh, and he loved this city, and everyone we spoke with stated he was a person of faith and a person that believed in God and believed in living out the life of a godly person.’

NYPD Commissioner Jessica Tisch also said that Islam ‘died as he lived: a hero.’ 

‘He was doing the job that we asked him to do. 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 the city,’ Tisch added. 

‘I want to extend my profound sympathies to all of the victims and their families and to the brave NYPD cops who today lost a brother,’ she concluded. 

Patrick Hendry, the president of the Police Benevolent Association, called the loss ‘devastating.’

‘He was a hardworking police officer who was proud we know from hearing from his family to put on that uniform and shield of a New York City police officer, Hendry said.

‘Every day, he went out and did his job, and he went out every single day to provide for his family, whether it was overtime or whatever he had to do to provide for this family.’ 

In a statement, the New York Police Department also called Islam ‘the very best of our department.

‘He was protecting New Yorkers from danger when his life was tragically cut short today,’ the department said.

‘We join in prayer during this time of incomprehensible pain. We will forever honor his legacy.’

Officials have not released any further information about the others killed and injured in the massacre on Monday.

But New York Gov. Kathy Hochul said the state mourns ‘ four New Yorkers, including one of New York’s Finest, taken in a senseless act of violence. 

‘Our hearts are with their loved ones and everyone affected by this tragedy, and we honor the first responders who bravely ran toward danger.’

Mayor Adams added that the city is reeling as ‘four innocent families are mourning.’

He said that in addition to Officer Islam, the ‘city also mourns the three other innocent lives lost this evening and is praying for another innocent victim fighting for his life in critical condition. 

‘It’s unthinkable these people were taken from us so randomly and senselessly. They and their loved ones are in our hearts.’

Similarly,  New York Attorney General Letitia James added that she is ‘praying for our law enforcement and the New Yorkers impacted in the shooting situation this evening in Manhattan.’