The Beale ciphers
en.wikipedia.org
en.wikipedia.org
> Beale entrusted a box containing the encrypted messages to a local innkeeper named Robert Morriss
If it's just an unknown one time pad we're looking for, this is pretty damning:
> If the Declaration of Independence is used as a key for the first cipher, it yields alphabetical sequences such as abfdefghiijklmmnohpp and others
I happen to have several maps of that area from the 1820s through the 1920s.
If you ever get serious about it, give me a call :)