Apparently he had issues with the NFL's handling of CTE and the fact that he did it at the NFL HQ it sounds like he was maybe trying to send some type of message
Is the NFL doing enough to prevent and address CTE?
Should there be better support for retired players?
abcnews-go-com.cdn.ampproject.org
Is the NFL doing enough to prevent and address CTE?
Should there be better support for retired players?

Manhattan shooting suspect claimed to have CTE, mentioned NFL in note, sources say
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.