Shane Tamura, the Park Ave. gunman who killed an NYPD officer and three others before taking his own life, left behind a suicide note saying he suffered from CTE, a brain injury often linked to playing football, police sources said Tuesday.

Shane Tamura, 27, killed an NYPD officer and three other people on Monday evening when he stormed the Midtown skyscraper that’s home to the football league’s headquarters.

The 27-year-old man who shot and killed four people at a Midtown office building on Monday carried a note in his pocket claiming he suffered from CTE, asked that his brain be studied and made references to the NFL.

Tamura was involuntarily held after being considered a danger to himself or others, according to a law-enforcement official.

New York City Mayor Eric Adams said on “Morning Joe” on MSNBC there is belief Tamura may have been targeting the NFL office in the building.

Shane Tamura said he had CTE. His claim, which is unproven, has again put a spotlight on the NFL's troubling history with its players and the disease.

New York City Mayor Eric Adams says that a gunman who killed four people at a Manhattan office building was trying to target the headquarters of the National Football League but took the wrong elevato

Compared to what’s on the news, I don’t think any one of us, none of my teammates, sensed anything like this from Shane,” the former teammate told The Post.