The head of the New York Police Department said that investigators plan to question a man who supplied parts for a gun used in the attack on Monday.

Four victims, including an NYPD officer and a Blackstone executive, were killed in an NYC shooting at 345 Park Avenue.

Tamura worked as a surveillance department employee at the Horseshoe hotel and casino in Las Vegas, a spokesperson for the Horseshoe said on Tuesday. Several squad cars from the Las Vegas Metro Police were seen at the entrances to a gated neighborhood where Tamura was believed to have lived.

The killing of four people including a police officer in a Midtown Manhattan office building rattled a city where mass attacks are rare and violent crime has declined.