Believe it or not, it was a book called American Pharaoh. It's about Chicago's previous Mayor Daley. (The current Mayor Daley - or "da Mare" - is his son) The book eluded slightly to mob ties, but didn't go into them very much. I was very much in a civic pride frame of mind and reading as many books about Chicago as I could. Then I read the book "The Outfit" by Gus Russo. From there I just went nuts with it.