The man who police say fatally shot four people in Manhattan and who New York City Mayor Eric Adams said Tuesday was targeting the offices of the National Football League claimed he suffered from a degenerative brain injury caused by repeated brain injuries and trauma.

Police say that gunman Shane Tamura, 27, had a three-page note in his wallet saying he suffered from a brain disease and was requesting that the league study his brain. Although repeated brain trauma can lead to CTE, the disease can only be definitively diagnosed after death.

Experts do not believe CTE is linked to one single brain injury, according to the Mayo Clinic. However, in many cases, it is related to repeated head injuries, like concussions, which may be linked to contact sports such as football or to military combat.

Tamura played high school football outside of Los Angeles, according to the Los Angeles Times, but did not play beyond that level.

Police said Tamura shot himself in the chest rather than in the head, according

© The Hill