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.

Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday. Among those killed was an officer who was a dad of two with a third on the way.

An NYPD officer, a Blackstone executive, a Rudin Management associate and a security guard were killed in the shooting at Manhattan's 345 Park Avenue.