The gunman who killed four people at an office building in New York City on Monday evening left his home in Las Vegas, Nevada late last week.

The man who opened fire in a Midtown Manhattan office building, killing four people and wounding a fifth, appeared to be targeting the NFL headquarters and had a note claiming he suffered from CTE, police sources told ABC News.

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.