Brain experts say it could take weeks to learn whether Shane Tamura, the 27-year-old gunman who killed four people at a Manhattan office building before killing himself Monday, had chronic traumatic encephalopathy, a degenerative brain disease that can be diagnosed only after someone has died.
The process of testing for CTE, according to brain researchers and experts who spoke with ESPN, involves preserving, dissecting, staining and examining tissue samples from different regions of the brain under a microscope.
"That process can be a week, two [weeks]," said Dr. Brent Masel, a neurologist on the board of the Brain Injury Association of America. "... So there will not be an instant answer to that."
Investigators believe Tamura, a Las Vegas casino worker, was trying to get to the NFL offices after shooting several people Monday in the building's lobby but entered the wrong set of elevator banks.
Tamura, who played high school football in California roughly a decade ago but never in the NFL, had a history of mental illness, police said.
A note found in Tamura's wallet suggested he suffered from CTE and held a grievance against the NFL. In the note, he repeatedly said he was sorry and asked that his brain be studied for CTE, according to police.
Asked whether Tamura would be tested for CTE, New York City Mayor Eric Adams told CNN that the city's medical examiner would make that determination. The City of New York Office of Chief Medical Examiner told ESPN in an email Tuesday that an "examination of brain (neuropathology) is part of the complete autopsy process."
"Additional testing for the complete autopsy record ... will be ongoing," but the City of New York Office of Chief Medical Examiner did not respond when asked about the timeline for testing, which includes the examination of the brain.
Whether the gunman is diagnosed with CTE or not, experts cautioned against drawing direct connections between the shooting and the disease.
"Multiple factors" come into play, Dr. Julia Kofler, a neuropathologist at the University of Pittsburgh, told ESPN, noting that "we don't really know how they relate to each other."
"I think the connection between CTE and these acts of violence, it's impossible to really infer a causal relationship," Kofler told ESPN. "There are so many individuals with CTE who don't commit acts like this."
Kofler said CTE "in some cases" could be easier to diagnose in a younger person because their brains don't yet have aging-related changes.
Masel said that it was important to know that not everyone who has had multiple brain injuries is going to develop CTE.
"We certainly hope that nobody would just assume that if you've played football and you have psychiatric issues, you have CTE and the NFL is at fault here," Masel said.
For researchers to obtain tissue samples, Kofler said, consent from the family usually is required and that different medical examiners have different policies surrounding research.