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

Authorities say the man who killed four people at a Manhattan office building bought the rifle he used in the attack and the car he drove across country from his supervisor at a Las Vegas casino

The man who stormed a Manhattan office tower with a gun, killing four people before killing himself, worked in the surveillance department of a Las Vegas casino, part of an industry built on watching for threats before they unfold.