A married father of two with a third child on the way, the 36-year-old was working a New York Police Department-approved private security detail, in uniform, when he and three other people were killed Monday at the Manhattan skyscraper that houses the NFL's headquarters and other corporate offices.

The 27-year-old gunman fired indiscriminately throughout the building’s lobby and 33rd floor, killing Islam, security guard Aland Etienne, Blackstone executive Wesley LePatner and Rudin Management associate Julia Hyman before turning the gun on himself.

Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday. The injured victim was an employee at the NFL, according to NFL Commissioner Roger Goodell. Here's what we know about the four people killed: