And there isn’t. If prosecutors file a new case against a second person for the same crime, and get a conviction, there’s no mechanism by which that second conviction overturns the previous conviction. Depending on the circumstances, the first person convicted may not even have grounds to have their case brought before a court to be re-examined.
Then I don’t know what I can say more clearly. If they convict Mangione, and the real killer confesses, they can convict the real killer, too. They wouldn’t even have to free Mangione to do it.