The NYPD continues to work with investigators across the country to learn more about the gunman in Monday's deadly Midtown office shooting.

Didarul Islam, who was expecting a third child with his wife, was one of four people killed in Monday's shooting at an office building.

Businesses across the U.S. are reevaluating security after a shooting at a New York City office building raised concerns about workplace safety. The attack on a seemingly secure tower left four people dead and has companies desperate to prevent similar incidents.