This quote must have come from the movie. The original novel's version is even bettter: "Lawyers can steal more money with a briefcase than a thousand men with guns and masks.” [Don Vito Corleone to his son Santino]

I recommend reading the entire novel, and, while doing so, look for subtle hints dropped by Don Vito, especially, as to the way the Sicilian mafiosi had come to understand their need to avoid all government interactions. They operate as an invisible nation within another nation with their own police and judicial power, moral code, business code, etc.