Shane Tamura is suspected of shooting four people in Midtown Manhattan, where the NFL offices are. A note he left references the NFL and CTE.

The gunman in the deadly Midtown Manhattan shooting, Shane Tamura, wrote about the brain disease CTE in a note obtained by investigators.

CTE is defined as a progressive neurodegenerative disease that causes brain damage similar to what’s seen in patients with Alzheimer’s disease, per the National Institutes of Health (NIH). There is a known link between repeated head trauma, contact sports, and the development of CTE.