Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday.

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.

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.