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.

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

Family, friends, and colleagues are mourning an NYPD officer who was killed in a mass shooting in a Manhattan building Monday evening. Officer Didarul Islam, 36, was on duty working a private security detail when he was fatally shot in the lobby at 365 Park Ave.