'Clearly not in their right mind': CTE doctor on NYC gunman

(NewsNation) — One day after the shooting in New York City that left four people dead, the possibility that chronic traumatic encephalopathy played a role in the attack has become a hot topic.

Shane Tamura, the alleged shooter, had a three-page note in his wallet saying he suffered from a brain disease and was requesting that the National Football League study his brain, according to police.

Written on Tamura’s note were several names, including Dr. Christopher Nowinski.

Nowinski, a former pro wrestler and now neuroscientist and CEO of the Concussion Legacy Foundation, joined "Elizabeth Vargas Reports" on Tuesday and said that "it's hard what to make" of his name being in the note.

"With somebody who's willing to perform an act like this, I mean, they're clearly not in their right mind," Nowinski said. "So it's also unfortunate to consider that this sort of thing has happened before."

Nowinski began his work towards studying CTE over 20 years ago when his colleague at World Wrestling Entertainment, Chris Benoit, confided in him regarding concussion concerns.

Benoit didn't receive any help and eventually killed his wife, son and himself. That situation, and the one that occurred with Tamura, has Nowinski reinforcing that CTE is truly "a life-and-death issue."

"We don't know if this individual has CTE," added Nowinski. "But, big picture, CTE and traumatic brain injuries are very complicated and devastating issues."

Police said Tamura shot himself in the chest, which is of note, since he might have been trying to preserve his brain so scientists and doctors can look at it. It's also been said that CTE can only be diagnosed after death with an autopsy.

However, Nowinski argued that even after the autopsy, it still might not be determined if CTE is what caused Tamura's actions.

"You can't tie any brain injury or brain disease or medical condition to a single act, a single behavior," he said.

"So whatever the medical examiner discovers, it's not going to answer all the questions. It might give us a window into how impaired his brain was."