The New York City office building that was the site of a mass shooting Monday had significant security measures in place.

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.

NEW YORK -- A 27-year-old man wearing body armor and carrying an M4 assault rifle shot and killed four people, including off-duty New York Police Department Officer Didarul Islam, who was working security in a Midtown Manhattan office building, officials said during a press conference Monday evening.

This is a breaking news story. For latest updates, please go to our live blog. An NYPD officer and at least four other victims were killed in a shooting at an office skyscraper in midtown Manhattan Monday evening,