The alarm reached Jon Gray on the 44th floor, in his C-suite office high above Park Avenue: An active shooter was in the building.In the lobby below, a gunman had opened fire, killing a uniformed police officer and two others who worked in the office tower.

The glittering skyscraper where hundreds work became the scene of New York City’s deadliest gun attack in 25 years when a man entered the lobby and started shooting.

A suspect was spotted entering the Blackstone building holding an assault weapon. Get updates on the developing situation.

Employees at firms including Blackstone and KPMG hid and set up barricades during the gunman’s rampage.

Park Avenue is home to several high-profile tenants, making it one of the most prominent office addresses in Midtown Manhattan. The building serves as the global headquarters of Blackstone Group, occupying more than a million square feet across approximately 28 floors.

Blackstone's BREIT CEO Wesley LePatner is one of the victims of the shooting spree at 345 Park Avenue that also killed an NYPD officer.