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.

The gunman who opened fire at a Manhattan office building Monday, killing four people before taking his own life, legally purchased the rifle used in the attack, according to an attorney for the Las Vegas casino supervisor he bought it from.

New York City investigators believe a co-worker of the Las Vegas man who killed four, including a police officer, provided a component of the deadly weapon, the 8 News Now Investigators have learned.