New evidence can re-open a case, but to do so requires convincing a judge that the new evidence is so overwhelming that the case should be re-opened. (At least in the US.)

For example, I get off on the charge of murdering 999. I walk away, having been found not guilty. Thirteen years later it's found that not only did the cartridge cases have my fingerprints on them, but no fewer than four surveillance cameras show the entire thing in full color (colour, because it happened in Canada) and the RCMP was found to have falsified DNA evidence.

A judge would, and should, reopen the case.

But it MUST be tried, as all cases must, by an unbiased jury who judges ONLY on the evidence presented. In my first trial, someone told someone else that their hairdresser's second cousin's boy friend's best friend was convinced I did it. That's not evidence and should not have been admitted (much less have come to trial). Now, if 999 had said to a cop and the EMT who was trying to plug the holes that I had shot him, that's the ONLY acceptable hearsay because it's a dying declaration. (If you want to get someone in trouble, wait until you're dying and there are witnesses around, the downside is that you really have to die).

Ignorant jurors? No. But they have to judge by the evidence presented, not by anything else.

Remember, a verdict of "Not Guilty" does not mean "This person is innocent of this crime."