Mary-Ann: Stewart's COMMITTEE OF VIGILANCE is definitely non-fiction. He uses a research/narrative technique that I really find effective: using and quoting from the contemporary newspaper reports of the day. Worth the search effort to find it and read it.
Also, and for something entirely different,I recommend Kevin Mullen's THE TOUGHEST GANG IN TOWN. Mullen is a retired SFPD deputy chief who has a love affair with the history of his department. This is a collection of "TRUE CRIME" stories of San Francisco.