The gunman who had suspected he had CTE when he shot several people in a Manhattan office building did in fact have the disease, the New York City medical examiner said Friday.

The shooter, Shane Devon Tamura, 27, who played high school football, shot and killed himself after fatally shooting four people in July. The medical examiner said he had “unambiguous diagnostic evidence” of low-stage CTE, or chronic traumatic encephalopathy.

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The brain disease is caused by repeated head injuries and is most commonly associated with players in the NFL. Medical professionals have said young athletes can develop CTE even if they do not go on to play football after high school. 

New York officials said Tamura was targeting the headquarters of the NFL when he opened fire at the office building, which housed the NFL headquarters. 

Tamura killed Didarul Islam, a New York Police Department officer; Aland Etienne, a security guard behind a desk; Wesley LePatner, a senior executive at Blackstone; and Julia Hyman, who worked at Rudin Management. The gunman also shot and wounded Craig Clementi, an employee for the NFL.

CTE often affects the superior frontal cortex, which controls cognition and executive function, and oftentimes affects the amygdala, which is needed in emotional control, aggression, and anxiety.

The NFL first acknowledged the link between CTE and football players in 2016. The NFL said in a statement Friday it continued 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,” the statement added.

The brain disease can only be diagnosed after death, as there is no current technology that can detect CTE when a person is alive. This has made CTE difficult to study. 

Several former NFL players have had severe cases of CTE. 

Former New England Patriots tight end Aaron Hernandez had one of the worst cases of CTE, Boston University medical experts said. He died by suicide at age 27 after being convicted of murder. 

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In 2021, former cornerback Phillip Adams fatally shot six people before committing suicide. He was also found to have had CTE.

Former NFL player Dave Duerson notably shot himself in the chest in 2011 to preserve his brain. He left a note asking that his brain be studied after his death.