Originally posted by junior
In the US, once you're found Not Guilty, you cannot be tried again. There have been instances where people admitted to the crime well after the trial (one instance involved a writer who paid a sum of cash to two white men who had been involved in the lynching of a black kid in the south), but even in those instances, the law can't touch the individuals involved. The concept is known as Double Jeopardy in the US (and British) legal system, and is forbidden by the Bill of Rights. A person can only be retried if the jury can't come to a unanimous decision.
As far as the Innocent vs. Not Guilty thing goes, I think the best way to look at it is both ideas are correct. A person is "innocent until proven guilty" in the US legal system, and thus its necessary to prove that they are guilty. But this also means that the burden of proof is on the prosecution, and that, combined with the "reasonable doubt" standard (as opposed to "preponderance of evidence, which is used in civil trials), means that its entirely possible for a guilty individual to get a not guilty ruling even if jurors suspect that the individual really did do what he or she was accused of - so long as there's reasonable doubt that the suspect didn't do it.