The suspected shooter who killed four people in a Manhattan skyscraper Monday claimed to suffer from the brain disease Chronic Traumatic Encephalopathy, or CTE, which experts say could explain his violent behavior.

Shane Tamura, 27, is accused of driving from Las Vegas to New York City, entering an office building that houses major financial firms and the National Football League and killing four people before shooting himself. 

In a suicide note Tamura reportedly had in his pocket, he criticized the NFL and claimed to suffer from CTE, a neurodegenerative disease most commonly seen in athletes who have suffered repeat concussions and brain injuries, which can lead to permanent brain damage.

Tamura was once a talented football player and his note, revealed by a source to CNN, stated: ‘Terry Long football gave me CTE and it caused me to drink a gallon of antifreeze,’ referring to the former NFL player who was diagnosed with CTE and died by suicide after drinking antifreeze in 2005.

Authorities have also said Tamura, 27, had a ‘documented mental health history’ and in the car he was seen exiting before the shooting, they found cannabis and Zoloft, an antidepressant, though it isn’t known if Tamura was consuming either of those drugs.

Studies of American football players have revealed the consequences of repeated head trauma and traumatic brain injuries, including aggression, depression, impulsivity, psychosis, cognitive confusion, and premature death.

However, the only way to diagnose CTE is by an autopsy after a person has died, so there is no way to know if the alleged shooter had the condition. Tamura’s suicide note said he wanted his brain to be studied 

Dr Keith Vossel, a neurologist at the University of California, Los Angeles, told DailyMail.com: ‘Often, criminality is not really common with most of the neurodegenerative diseases – criminality or homicidal or suicidal behaviors – but they can occur.’

And while not all CTE sufferers will become homicidal or suicidal, those traits ‘seem to be more common in the syndrome that we associate with CTE,’ Dr Vossel added.

Suspected NYC shooter Shane Tamura, a 27-year-old private investigator from Las Vegas, was a former  football player who left a note in his pocket blaming his actions on CTE

Dr Vossel told this website: ‘We’re pretty sure that CTE is associated with impulsivity, sometimes suicidality, other mental health issues, due to strong association studies.

‘It’s really difficult to currently definitively prove the connection, but I think we’re on the right track.’ 

Dr Harrison Martland, a clinical pathologist, first named the condition ‘punch drunk’ in 1928, as it was more commonly seen in men who had entered and left the boxing arena multiple times.

Since then, research and understanding of the condition have evolved. Doctors have determined that repeated blows to the head generate tau, a small protein found in brain cells that can break off and cause harmful tangles. 

But there is no test to screen for CTE in living patients, and symptoms often mimic those of Alzheimer’s, PTSD, or Parkinson’s.  

Tamura was a former high school football player who left a note in his pocket blaming his actions and mental health crisis on CTE.

‘Study my brain please,’ the note said. ‘I’m sorry.’

Dr Carole Lieberman, a board-certified psychiatrist, told DailyMail.com: ‘What stands out in this case is how the NYC gunman chose to shoot himself in the chest rather than the head. 

‘This highly unusual decision suggests he wanted his brain preserved for autopsy, strongly indicating he believed he had CTE and wanted it confirmed.’

NYPD Didarul Islam, a father of two with a third on the way, was shot and killed by suspected shooter Shane Devon Tamura

To determine CTE in deceased brains researchers look for a buildup of tau in certain parts, including the frontal lobe, which plays a crucial role in problem-solving, self control, emotion regulation, impulsivity, and aggressive behavior.

It is not known when, or if, an autopsy will be performed on Tamura.  

‘We know from other degenerative diseases like frontotemporal dementia that when the tau accumulates in regions that control our impulsivity and our social decorum… that can be associated with changes in personality and it can result in behaviors that can be disturbing for those around them,’ Dr Vossel said.

A 2024 study of nearly 2,000 former football players conducted by Harvard Medical School found that 34 percent think they have CTE, reporting more cognitive problems, depression, suicidal thoughts, chronic pain, and other issues not reported by people who did not believe they had CTE.

Doctors have found that hundreds of football players have had CTE over the years.

In 2023, the Boston University CTE Center announced that it posthumously diagnosed 345 former NFL players with chronic traumatic encephalopathy out of 376 retired players studied, equating to about 92 percent.

Dr Vossel added that not all CTE sufferers become homicidal, but the disease does lead to major personality changes: ‘Some people might start with more memory issues, and it’s maybe a different rate of decline. 

‘It could be slower, and it could be older people, and they could look like they have Alzheimer’s disease.’

Athletes with CTE showed damage in their brains, including enlarged ventricles, indicating a shrinkage in brain space, holes in brain tissue, thinning in key areas, and clogged blood vessels

He continued: ‘And then these more striking cases, the mental health issues tend to be occurring in younger people in whom it might be more difficult to disentangle any pre-existing mental health issue from CTE-related changes.’

In the past, NFL athletes who have taken their own lives or those of others have been confirmed post-mortem to have had CTE.

Several former players, including Dave Duerson and Junior Seau, died by suicide using firearms. Duerson and Seau intentionally shot themselves in the chest, like Tamura. 

Both former athletes were later diagnosed with CTE.  

Kansas City Chiefs linebacker Jovan Belcher shot and killed his girlfriend before driving to Arrowhead Stadium and taking his own life in front of his coach and general manager.

According to a post-mortem report, Belcher’s brain showed signs of CTE.  

And former New England Patriots player Aaron Hernandez was diagnosed with late-stage CTE after his 2017 suicide. He had been convicted of murder, having killed Odin Lloyd, a semi-pro football player, in 2015.

Memory and thinking problems were the strongest predictor of CTE. Other key factors included low testosterone (1.4x more likely), concussion symptoms (1.3x more likely), and depression, mood swings, or chronic pain (slightly increased risk)

In the final years, Hernandez became increasingly paranoid, convinced that people were out to kill him.

Dr Lieberman said: ‘The connection between neurological injury and sudden acts of violence should not be underestimated.’ 

It is unclear whether Tamura suffered from symptoms linked to CTE, such as cognitive issues. 

And a post-mortem won’t be able to detect if he also had a mental health condition, like depression, or separate any mental health issues he was contending with from symptoms, and consequences, of CTE.  

Dr Lieberman added: ‘Clinical signs, such as mood instability, paranoia, aggression, and suicidal ideation, combined with a history of repeated head trauma, often point to it. 

‘In this case, his behavioral spiral fits the pattern.’