There is already a question on this site asking about saving a person from being executed (fairly) by a beis din, as well as a question regarding the criminal himself, if he may/must attempt to save his own life instead of being killed.
IMHO, the answers to these two questions are definitely not, as a penal system cannot possibly work that way (and because everyone is obligated in ובערת הרע מקרבך to some extent), but one would be hard pressed to find an explicit source addressing the issue because of its obvious answer.
However, I wonder if any sources specifically address the case of an innocent person1. If I know with absolute certainty that Reuvian is not guilty of a crime (punishable by death) for which he was convicted by a Beis Din, and this Beis Din is on their way to executing him, can I intervene? Let's say that I cannot convince the Beis Din otherwise, such as a case where there was already a psak din that Reuvain was guilty of being a meisis. Can I help Reuvain run away and provide him with sanctuary?
1. This is in bold to indicate that I'm looking specifically for sources that address this issue, and not for anyone's 'diyuk', though you're welcome to share it in the comments section