AN apparent suicide note has revealed what could be the chilling motive behind why a gunman attacked a New York City skyscraper.

Shane Tamura was found by cops having shot himself in the chest after he killed four in the horror attack just a 20-minute walk from Times Square on Monday.

Cops are now desperately trying to piece together why he carried out the sick shooting on 345 Park Avenue but believe they might have an answer, the New York Post reports.

A three-page note was found on Tamura’s body that horrifically presented a health battle caused by American football as his excuse.

According to CNN, he wrote in it: “Terry Long football gave me CTE and it caused me to drink a gallon of antifreeze.

“You can’t go against the NFL, they’ll squash you.

“Study my brain please I’m sorry Tell Rick I’m sorry for everything.”

Tamura wrote that he suffered from the neurodegenerative disease chronic traumatic encephalopathy (CTE).

CTE is linked to repeated head trauma and is only diagnosed through an autopsy of the brain.

CTE has been a major issue for the NFL with a number of former players with the disease committing atrocious acts of violence.

Terry Long, a former football player for the Pittsburgh Steelers, died by suicide after drinking antifreeze in 2005.

Another horror case of CTE-violence was when former NFL tight end Aaron Hernandez was convicted of murdering Odin Lloyd in 2013.

Former San Francisco 49ers cornerback Phillip Adams was also diagnosed with a CTE after he killed six people and then himself in an April 2021 shooting spree.

Tamura had played football at high school in California where he was said to be a standout player.

But former classmate Caleb Clarke told NBC that Tamura hadn’t lived up to the promise he had shown.

He said about his former classmate: “The only thing I can really think of is there was a point where it looked like the sky was the limit, and then it wasn’t anymore.”

What is CTE?

CHRONIC Traumatic Encephalopathy is known as a brain condition that is often linked to repeated head trauma.

The condition is diagnosed after death and is commonly found in pro-sports players due to concussions.

Some symptoms of CTE include memory loss, confusion, impaired judgment, depression, anxiety, suicidal thoughts, and progressive dementia.

These signs can begin to appear after years or even decades after the last brain trauma.

A CTE scan is used to diagnose the brain disease after someone has passed away as there is no test to run while someone is alive.

Doctors often slice brain tissue and use special chemicals to make the abnormal tau protein visible to examine for patterns related to CTE.

The NFL occupies floors five to eight in the building – raising the possibility that he was targeting the sports organisation in the horror attack.

But, Tamura shot and killed three in the lobby and then rode the lift to the 33rd floor offices of the company that owned the building, Rudin Management.

The shooter got into an elevator after he spared a woman who had been inside the lift set to go up to the 33rd floor, according to CNN.

Tisch said there were no indication that Tamura had prior connections to the real estate industry.

Tamura had a history of serious mental health issues, according to NYPD Commissioner Jessica Tisch.

Initial checks on the FBI’s internal system found no information about Tamura, the New York Times reported, suggesting he doesn’t have a previous criminal record.

The shooting happened in the same area of the city as where the United Healthcare CEO Brian Thompson was killed.

NFL commissioner Roger Goodell said an NFL employee was seriously hurt in the violence.

Goodell said: “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.”

Other notable CTE-related deaths include the NHL’s Todd Ewen who died by suicide in 2019 and the NFL’s Ken Stabler who passed away in 2015 and was later diagnosed with a high Stage 3 CTE.

Workers desperately ran for their lives in suits while those trapped in Blackstone’s office built a barricade across the door with furniture.

One off-duty NYPD cop and three civilians have tragically been killed in the shooting while a fifth person was wounded.

The Wall Street Journal is reporting that a Blackstone chief was among those killed.

CCTV caught him exiting a double-parked BMW with an M4 rifle and walking across a public plaza into the 44-story building.

The crazed gunman – clad in a bulletproof vest and with a silencer on his weapon – then sprayed the lobby with gunfire and killed the off-duty officer working a corporate security detail.

The NYPD named the off-duty officer killed as Didarul Islam and paid tribute to the man who “represented the very best of our department”.

The department said: “He was protecting New Yorkers from danger when his life was tragically cut short today.

“We join in prayer during this time of incomprehensible pain. We will forever honour his legacy.”

Tisch said of Islam – an immigrant from Bangladesh – that he “died as he lived. A hero.”

“He was doing the job that we asked him to do. He put himself in harms way. He made the ultimate sacrifice.”

If you or someone you know is affected by any of the issues raised in this story, call or text the 988 Suicide & Crisis Lifeline at 988, chat on 988lifeline.org, or text Crisis Text Line at 741741.