I gave this book until halfway before dropping it. Too much of it consists of, essentially, lists of vocabulary words with no context or explanation. Many of the chapters are two pages long, like the one for private investigators, while there's a lengthy listing of every sub-branch of the Los Angeles Police Department that goes on for pages and pages. From that chapter, I gathered that those sub-departments have confusing and overlapping jurisdictions. That's nice, but it could have been condensed to a few sentences, and left plenty of room to discuss how such a complicated structure could interact with officers, PIs, or amateur sleuths trying to solve a crime. Huge topics like "crimes of passion" get a paragraph. There seems to be no pattern to which ideas get long lists of names and which are barely mentioned. Honestly, avoid this book unless you get it for essentially free. Maybe it was a good reference when it was originally published, but now it offers nothing Wikipedia couldn't give you. (Which is not to say that any writer's research should end with Wikipedia, only that there must be better references out there.)
The justice system is a large, confusing thing. This breaks that down for you. Great for mystery writers even to the casual reference in a fiction book. I found this book at a garage sale and have never regretted it. :)