The Omniscient Truth?

One little part of Aristotle's On Rhetoric that I found particularly interesting and thought about for a while was this idea he presents that people are naturally inclined to know truth when we hear it. He says, "But rhetoric is useful because the true and just are by nature stronger than their opposites..."(34). The footnote tell us that Aristotle believed truth was grounded in physis (nature), and it gave me the impression that Aristotle's form of truth was something that if people hear it against another argument, they would be almost physically moved accept that truth. I have to wonder if this is true. This idea certainly supports Aristotle's idea that there is a Supreme and Universal Good that all people have a connection to. I have a hard time with this because even Aristotle says that rhetoric can be used irresponsibly to sway audiences with tactics that prey on their emotions. When someone can speak in a way that makes one feel pity or grief, couldn't that be easily mistaken as truth grounded in physis? I think the most prevalent examples today would be people who are wrongly convicted of a crime and then later vindicated by a DNA test or some other kind of new evidence. In these cases, at least at first, an untrue version of events was decided to be true, and the jury is supposedly only to convict when there is no doubt. Also cases such as O.J. Simpson's or Casey Anthony's where most people would claim they know the truth of what happened, but in a court of law these individuals were proven innocent. I am not making a statement on their guilt or the quality of our court systems, however, I am saying that in matters such as these what is true is a murky and difficult thing to understand. Sometimes we can be mislead and reject the truth even though it's right in front of us. My point is that many things in our lives a properly constructed untruth can convince people just as well as the truth itself. I am confused by Aristotle's idea of truth because he gives classifications of what makes a good audience member. He categorizes them as someone with experience who will be able to discern what is true in the midst of many arguments that seem valid. My point is that for things like court cases the truth isn't necessarily relative, it's history something happened and the jury must decide who's telling the truth, and it would be incredibly foolish to go into that situation with the idea that "I'll know the truth when I hear it" because a skilled rhetorician can fool many people and have them accept a untruth as truth.