If they ever in the future find out Vinny wasn't really Jerry Callo, he will likely go to jail and Bill and Stan will likely have to have another trial.
The judge who lied about it for Vinny would get in trouble too.
Why would they have to have another trial? Despite not being an attorney with a long history behind him, he's still a licensed attorney and their innocence was basically proven. I would think the people of the county would riot against the judge and prosecutor if they knowingly tried to put the two in jail and let the real killers go free.
Since the charges were dismissed after the trial began, the case would be dismissed with prejudice, meaning the charges could not be filed again.
Also, let's be real here; after those experiences, what is the likelihood that Vinny, Lisa, Bill and Stan will ever return to Alabama? Or that anyone who is ever able to prove that Vinny was not Jerry Callo will ever happen to stumble upon that little town?
Think of all the people who had to rely on that lousy public defender. We can laugh at how bad he is because Bill and Stan can use Vinny instead, but most people go with a public defender because they have no choice.
The entire case (and a capital murder one at that) was built around a half dozen witnesses who were grossly mistaken. What else has this county's justice system been up to?
That's the least of the county's judicial problems. The cops and the court have a laundry list of very illegal procedure violations. Just a few examples include not allowing an attorney to practice purely because of discrimination, excepting an informal confession, and the prosecutor not giving the defense any of the collected evidence until he asks. In the real world, the whole county's judicial system would probably be shut down for a time once outsiders found out just how bad it was.
The flimsiness of the eyewitness testimony in general, while laughable here, reflects the real-world issues with eyewitness testimony, which was the cornerstone to legal cases for centuries, and is still a key factor today. How many other innocents like Bill and Stan have been prosecuted based on such flimsy testimony and didn't win their cases?
Immediately after the sheriff testifies, the prosecutor looks very nervous for a minute, before standing up and announcing with a huge smile on his face that he's moving to dismiss all charges. Once he got over his embarrassment, he had every reason to be excited - not only were the real criminals found, but he'll probably be the one to charge the recently arrested killers, and it's shaping up to be the easiest case of his career. Earlier in the film, he told Vinny that the only thing that would have made his case stronger was to have the murder weapon, and now he does; he knows all the possible weaknesses the next defense attorney might try to exploit in his witnesses' testimony; and on top of that, he is now certain that only the Tempest could have made the tire marks left at the scene and can call another automotive expert to testify to that, getting a slam-dunk win in a capital murder case.
Judge Haller is already a big stickler for the rules, but Vinny's lie that he's been practicing for 16 years doesn't help. While he had to lie to be allowed to work his cousin's case, it makes his lack of practice or knowledge of procedure look like flagrant disrespect, because a lawyer practicing for 16 years would know better.
