Here's what to know about CTE, the brain disease the NYC shooter blamed
for his mental health issues
[September 27, 2025]
By JIMMY GOLEN
BOSTON (AP) — The degenerative brain disease that has besieged the
National Football League for two decades with a billion-dollar lawsuit,
congressional hearings, an A-list movie and an unrelenting cortege of
ex-players’ obituaries intruded on America's favorite sport in the most
violent manner yet when a gunman who turned out to have the disease
killed four people earlier this year.
At the time of the July 28 attack, Shane Tamura, the Las Vegas casino
worker who targeted the New York City skyscraper that is home to the
NFL’s headquarters, carried a note blaming the league for his mental
health problems.
Tamura, 27, who played football in high school, said in a three-page
note found in his wallet that he had chronic traumatic encephalopathy —
diagnosable only after death — and implored those who found him: “Study
my brain.” Among his grievances against the NFL was a claim that the
league put its profits ahead of player safety by concealing the harm CTE,
and football, can cause.
On Friday, a New York City medical examiner reported that Tamura, who
fatally shot himself in the chest after the rampage, had “unambiguous
diagnostic evidence” of low-stage CTE.
A degenerative brain disease that has been linked to concussions and
other head trauma common in military combat and contact sports, CTE has
been diagnosed in more than 100 former NFL players and arisen as an
existential threat to the United States’ most powerful pro sports
league.
Here is what we know and don’t know about the connection between CTE,
the NFL and the shooter.
What is CTE?
Chronic traumatic encephalopathy can affect regions of the brain
involved with regulating behavior and emotions. This can lead to memory
loss, depression, violent mood swings and other cognitive and behavioral
issues, though researchers note that these symptoms can also be linked
to other illnesses.
Experts say symptoms can arise years or decades after the last brain
trauma. Evidence of the disease has been found not just in those with
long professional careers but in high school athletes as well.
Its dangers have led some states to consider banning youth football,
prompted leagues at most levels to limit contact drills in practice and
spawned a series of concussion protocols and other rule changes designed
to take the most violent edges off the hard-hitting sport.
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Ann McKee, director Boston University's center for research
into the degenerative brain disease chronic traumatic
encephalopathy, or CTE, addresses an audience on the school's campus
Nov. 9, 2017 about the study of NFL football player Aaron
Hernandez's brain, projected on a screen, behind right, in Boston.
(AP Photo/Steven Senne, File)
 Why is it associated with the
NFL?
Researchers have established a connection between CTE and contact
sports, military combat and other activities with repeated blows to
the head. After more than a decade of denial, the NFL conceded the
link between football and CTE in 2016 testimony before Congress, and
has so far paid more than $1.4 billion to retired players to settle
concussion-related claims.
The 2015 Will Smith film “Concussion” detailed the pioneering
efforts of forensic pathologist Bennet Omalu, whose diagnosis of CTE
in Pittsburgh Steelers Hall of Fame center Mike Webster was the
first in a former NFL player. Hall of Famers Ken Stabler, Frank
Gifford and Junior Seau have also been diagnosed with CTE, as has
Aaron Hernandez; in a 2017 paper, evidence of the disease was found
110 of the 111 former NFL players' brains studied.
What did the medical examiner find?
CTE can only be diagnosed definitively by examining the brain
posthumously through an autopsy.
The medical examiner’s report determined that Tamura suffered from
the degenerative brain disease but did not reach a conclusion on the
cause of the disease.
“CTE may be found in the brains of decedents with a history of
repeated exposure to head trauma,” the report said. “The science
around this condition continues to evolve, and the physical and
mental manifestations of CTE remain under study.”
Tamura didn’t play professional football but played during his high
school years in Southern California, where he grew up.
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Associated Press writers Maryclaire Dale, Laura Ungar and Josh
Offenhartz contributed to this story.
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