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.

Shane Devon Tamura was the 27-year-old man living in Las Vegas who fatally shot at least four people in a mass shooting at 345 Park Avenue in New York City on July 28. Here's what to know about the N.