In Star Wars Annual 1, Rebel intelligence agent Eneb Ray foolishly attempts an assassination of Emperor Palpatine, which goes about as well as one might expect:
Notably, though, he actually survives, and shows up in at least one future episode of the Star Wars comics. While some (such as Bail Organa) might have had reason to suspect Palpatine’s Sith affiliations, certainly the information was not widely known. Did Eneb Ray ever attempt to inform the Rebellion leadership of Palpatine’s true nature? And if (as it seems) he didn’t, why not?