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

Bankers and traders returned to work on a somber Tuesday morning in Midtown Manhattan, New York's financial epicenter, one day after a shooting that killed four people, including a senior Blackstone executive.

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.