Police searched Shane Tamura’s employee locker at a Las Vegas Strip casino in their attempts to piece together why he killed four people and then himself in New York City earlier this week, the 8 News Now Investigators have learned.

The New York City Police Department sent detectives to Las Vegas to work with the Bureau of Alcohol, Tobacco and Firearms to execute search warrants and continue the investigation into Monday's deadly shooting inside a Midtown Manhattan office building.

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.