The gunman who killed four people, including an NYPD officer, reportedly had a grievance against the NFL and blamed football for issues with CTE.

The gunman, Shane Tamura, may have suffered from chronic traumatic encephalopathy and played high school football in California.

A gunman who killed four people at a Manhattan office building before killing himself claimed in a note to have a brain disease linked to contact sports and was trying to target the National Football League's headquarters but took the wrong elevator,