The mass shooting at a Manhattan office building raises new concerns for business leaders looking to secure their staff and buildings from threats.

The funeral will be held Thursday for the police officer who was one of four people killed in Monday's mass shooting at a Midtown Manhattan office building.

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.