A gunman who murdered four people in a New York office building before taking his own life had CTE, a degenerative brain disease which has been linked to playing American football.
It is believed Shane Tamura targeted the skyscraper in Manhattan because it houses the headquarters of the NFL.
The 27-year-old, who played high school football, had "unambiguous diagnostic evidence" of low-stage CTE, or chronic traumatic encephalopathy, the New York City medical examiner said.
In a three-page note discovered by police after the mass shooting, Tamura made repeated references to CTE.
In his note, which was written on notepad paper and using a variety of ink, Tamura wrote "CTE study my brain please. I'm sorry." And again: "Please study brain for CTE. I'm sorry."
He also specifically refers to Terry Long, a former NFL player who starred for the Pittsburgh Steelers. Long was diagnosed with CTE after drinking antifreeze to take his own life 20 years ago. CTE can only be diagnosed after death via post mortem.
In a statement, the NFL said: "We continue to grieve the senseless loss of lives, and our hearts remain with the victims’ families and our dedicated employees.
"There is no justification for the horrific acts that took place. As the medical examiner notes ‘the science around this condition continues to evolve, and the physical and mental manifestations of CTE remain under study’."
A Sky News investigation last year explored the link between CTE and violent attacks, including mass murder.
We looked at the case of former high school football player Noah Green. He was 25 when he crashed into a security cordon protecting the capitol building in Washington DC and stabbed police officer William Evans to death, before he too was shot dead by responding police.
Green's mother, Mazie, told me she believes his crime was caused by brain injuries sustained on the American football field. He also had CTE.
The theory of a link between CTE and violent crime is increasingly cited in the courtroom.
Kellen Winslow, a former NFL player, argued for his sentence for multiple rapes to be reduced because of head trauma suffered on the football field.
Former San Francisco 49ers star Phillip Adams shocked the country when he shot dead six people, including grandparents and their two grandchildren, then himself in 2021. He had severe CTE.
(c) Sky News 2025: Gunman who targeted NFL HQ 'had brain disease that's linked to playing American foot
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