The NYC shooter said his brain was damaged by football. Here’s what we know about CTE.

On Monday evening in Midtown Manhattan, a 27-year-old gunman opened fire in an office building that houses NFL offices, killing four people, including a police officer and then himself. In a note left in his wallet, the shooter referenced chronic traumatic encephalopathy, commonly called by its initials CTE, and criticized the NFL for covering up the traumatic brain effects of playing football.

“Study my brain please,” read the note left by the shooter, who was a former high school football player, according to the New York Times. The Times reported that the note also included references to NFL players who had also committed violent acts and were then diagnosed with CTE after their deaths. The shooter shot himself in the chest rather than in the head, following the example of retired NFL