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.

Investigators plan to question a man who supplied parts for a gun used in the shooting at a Manhattan office building that houses the National Football League’s headquarters, New York City Police Commissioner Jessica Tisch said Tuesday.

Officials said the gunman fatally shot himself after his attack, which set off a chaotic scene that rippled out into the heart of Manhattan during rush hour.