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, and was targeting the NFL — but took the wrong elevator, officials said Tuesday.

A police officer and three other people were shot and killed, and one other injured, by a crazed gunman who stormed a swanky Midtown skyscraper early Monday evening — before turning the gun on himself,