So that I can google for it - what's the original text? Thanks!
The version I've read is "Tutte le verità sono facili da capire quando sono rivelate, il difficile è scoprirle!" But that sounds like suspiciously modern Italian to me, so I wouldn't be surprised to find out that it's itself a paraphrase.
ETA: Apparently it was quoted in Criminal Minds, season 6, episode 11, and I suspect the Italian dubbing backtranslated the English version of the show rather than looking for the original wording by Galileo. (Which would make my version above a third-level translation.)
ETA2: In the original version of Criminal ...
Here's the new thread for posting quotes, with the usual rules: