If you were going to pick ONE book to read on J. EDGAR HOOVER, which would it be?

[Buttmunker]

The time period alone that would be covered, and the rich characters he interacted with, and the many scandals he knew about - but I'm looking for more of a fact-based book as opposed to a tabloid-based book with no reference sources (author's "opinion" creeps in sometimes, which becomes more 'imagination' than responsible journalism).

I respected the book Helter Skelter by Vincent Bugliosi and Curt Gentry, so perhaps the best to start with would be Gentry's J. Edgar Hoover: The Man and the Secrets?

Any thoughts?