Might I interest you in a very good book on the topic of intelligence gathering during the Civil War?
You may want to check out the book, The Secret War For The Union: The Untold Story Of Military Intelligence In The Civil War, by Edwin C. Fishel, from your local library. The book is 734 pages long with extensive notes and references.
The author was in the intelligence business for thirty years, beginning in WWII and going on until he a chief intelligence officer at the National Security Agency (NSA) and then a director of the National Cryptologic School Press.
____________________ Belief does not make truth.
Evidence makes truth.
And belief does not make evidence.