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

Investigators believe Shane Tamura, of Las Vegas, was trying to get to the NFL offices after shooting several people Monday in the building’s lobby but accidentally entered the wrong set of elevator banks,

The 27-year-old man who shot and killed four people at a Midtown office building on Monday carried a note in his pocket, police sources told ABC News.