Once a promising athlete, the 27-year-old faded from public view—until he showed up at 345 Park Avenue, gun in hand.

Wearing body armor and wielding an assault-style rifle, the alleged gunman burst into a Midtown Manhattan office building shooting victims at random.

Investigators found the note in the wallet of 27-year-old shooter Shane Tamura who police said opened fire inside of 345 Park Avenue.

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.

Workers in the area received shelter in place warnings on their iPhone during the melee. But Tamura’s senseless attack in the heart of the city's business district highlights the need to protect the rank and file even more,

The alleged gunman at a shooting rampage in a midtown Manhattan office building was identified as 27-year-old Shane Tamura, of Nevada.