Excellent book by Tim Weiner *SNORT* who also authored the CIA history "A Legacy of Ashes" - which I previously recommended just prior to the great Rattoing.
The title is a bit misleading, there is virtually nothing on this book about police work. The author's focus is on the FBI's task of serving as a domestic intelligence agency, in particular the COINTELPRO program started by J Edgar Hoover to track anarchists, communists, homosexuals and anyone else he determined to be "subversive". Hoover's original intent was to compile a list of people who would be herded into detainment camps if WWIII were to break out. Later the focus shifted to trying to establish a link between the Soviets and the various leftist organizations the sprung up in the US during the 1960s.
This leads into Hoover's death, Watergate, the agency's attempt to shift to investigation of terrorism at home and abroad up to the present day.
Anyway, excellent read, and if you haven't read Legacy of Ashes you should check that out too.