I recently renewed my library card ( expired 17 yrs ago) and picked up a few books. Among them was Public Enemies by Bryan Burrough.
It is an excellent history book that reads like an exciting novel.
The book covers the 14 month crime spree of the most famous of the depression era gangs as well as the response of the then fledgling FBI. Several "legends" fall to fact in this book and several legends are affirmed as well. Some names are immediately recognizable such as Machine Gun Kelley, John Dillinger, Baby Face Nelson, Pretty Boy Floyd, Bonnie and Clyde, Melvin Purvis, and J. Edgar Hoover. Others that are not famous, but significant and worthy of being remembered include Sam Cowley, Charles Winstead, Frank Hamer, and Hugh Clegg among many others.
Almost every page ( of which there are 552 in the "story" portion and an additional 40 in the reference/index section) has footnotes that are backed up with sources. There are dozens of people named in the book and each has a source reference and most have footnotes with "what ever happened to" information. There are quite a few addresses included and it was fun to fire up google earth and find these places. I was amazed at the number of places described in the book that are still standing and functioning as they did 75 yrs ago. Not all of them, but a lot of them.
The book relied heavily on the FBI files that were released in the mid 80s as well as other books written during and about the early 20th century. The author claims that the FBI files contain over a million pages of information about the "War on Crime" era. Considering the depth of this book, I do not doubt that it is true. I am awe struck that the author was able to present these facts in such a manner that I wanted to keep reading, not just to ingest information, but to find out what happens next. This is an exciting book and I highly recommend it.

http://www.amazon.com/Public-Enemies-Americas-Greatest-1933-34/dp/1594200211 link provided for reference only.

I was struck by just how incompetent police work often was back then. I guess that was inevitable, since the agency was new and still finding its legs.