A New York police officer, a “beloved” security guard and a senior executive with investment firm Blackstone were among four people killed Monday when a lone gunman stormed a sprawling office tower in Midtown Manhattan and opened fire.

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.

Midtown Manhattan was somber and on-edge after a mass shooting at an office tower left four people and the gunman dead, including Blackstone Inc. executive and a New York City police officer.