The crazed gunman who massacred four people at the NFL’s headquarters building in Midtownwhile holding a note begging for his brain be studied for “CTE” actually had the tragic brain disease, the medical examiner’s office revealed Friday.

A posthumous examination of Shane Tamura’s brain showed the tell-tale signs of chronic traumatic encephalopathy, also known as CTE, officials said. 

“It is unambiguously there and it is what is known as low-stage CTE,” a spokeswoman with the city medical examiner’s office said. “We’re answering that question that many people wanted to know the answer to.”

The diagnosis came after Tamura, 27, an ex-high school football player who killed himself during the shocking July 28 mass shooting in a Park Avenue skyscraper, left a rambling suicide note contending he had CTE.

The note found in Tamura’s pocket railed against the NFL, blaming the football league for his struggles.

“Please study brain for CTE,” the note read. “I’m sorry. The league knowingly concealed the dangers to our brains to maximize profits,” the note read.

CTE is a rare brain disease caused by concussions and repeated blows to the head.

Symptoms include aggression and other behavioral problems, memory loss and, in the late stages, dementia. It can only be diagnosed by dissecting a patient’s brain after death.

Hundreds of former football players suffered from CTE, brain tissue scans have shown – including Terry Long, a Pittsburgh Steelers offensive lineman who killed himself in 2005 by swallowing antifreeze.

The note found on Tamura’s body referenced Long’s suicide.

Tamura never played in the NFL, but was a star running back on his California high schools’ football teams.

Former teammates and coaches said Tamura became a “completely different” person in the years since high school.

A trove of records showed he struggled with his mental health, with his frantic mother once telling cops he threatened to kill himself and that he suffered from a sports-related concussion.

Tamura drove from Las Vegas to target the NFL’s headquarters inside 345 Park Ave. with an AR-15-style weapon, officials have said.

He gunned down Blackstone executive Wesley LaPatner, security guard Aland Etienne and NYPD Officer Didarul Islam in the building’s lobby.

But Tamura failed to reach the NFL’s HQ, instead mistakenly taking an elevator to the building’s 33rd floor, where he killed Rudin Management employee Julia Hyman, before turning the gun on himself.

NFL representatives said the league continues to grieve the senseless loss of lives.

“There is no justification for the horrific acts that took place,” a statement from the NFL reads.

“As the medical examiner notes, ‘the science around this condition continues to evolve, and the physical and mental manifestations of CTE remain under study’.”

The medical examiner’s spokeswoman stressed that it’s unclear whether Tamura’s CTE actually led to the shooting.

“We’re unable — as I don’t think science would be able to at all at this point — to say what role CTE played in that particular incident, causing that incident,” she said. “We’re not saying that CTE is the cause of what happened at the Park Avenue shooting.”