Onlooker: I read two of your comments above. First one says "unless it is beyond reasonable doubt, you can't convict"; and the second one says "defense failed to create a reasonable doubt in prosecution witness accounts"..
I am somehow reading between your lines and finding that you believe in "guilty unless proven innocent" approach.
I think it should have been the other way round. Since the umpires didn't hear anything, therefore the Aussies should have been able to "prove beyond reasonable doubt" (as opposed to just create reasonable doubt) that there is something wrong with defense witness accounts.
And I can't see (I too am not a lawyer, but still) how a wicket-keeper can convince Procter that he heard something that the umpire didn't.