New York City is mourning an NYPD officer and three other people killed in Monday night's shooting inside an office building in Midtown Manhattan. Officer Didarul Islam was in uniform working as a security guard for a private company at the time of the shooting,

Multiple casualties as gunman opened fire in the lobby of the midtown Manhattan building on Park Avenue that is home to the Blackstone investment firm and other corporations before moving to other floors.

Officials said the gunman fatally shot himself after his attack, which set off a chaotic scene that rippled out into the heart of Manhattan during rush hour.