Commentaire sur Makkot 1:6

Until the judgement is finished. [The judgement] of the accused. Since he will be killed by their testimony, and afterwards they are zommemized.

Perjuring witnesses are not to be put to death until [after] the end of the trial.
Because the Sadducees say: “[Perjurers were put to death] only after the accused had [actually] been executed, as it says, “ A life for a life” (Deuteronomy 19:21).
The [Pharisaic] Sages said to them: “But has not it already been said “You shall do to him as he schemed to do to his fellow” (Deuteronomy 19:19) which implies when his brother is still alive?
If so, why does it say “A life for life”?
For it might have been that perjurers are liable to be put to death from the moment their testimony had been taken, therefore the Torah states “A life for a life” that is to say that they are not executed until [after] the termination of the trial.
Mishnah six discusses at one point in the judicial process the witnesses are proven to be perjurers in order for them to receive the penalty that they tried to impose upon the accused.
This mishnah contains a dispute between the Pharisees and Sadducees, two of the main Jewish sects that competed during the Second Temple period (until 70 C.E.). The issue at hand is when are the perjuring witnesses to be executed: after the trial or only after the accused has been himself executed. The Sadducees claim that perjuring witnesses are only executed if they have been successful in having the accused actually executed. In other words, the witnesses are executed not for intending to unjustly execute the accused but for actually doing so. Just as in a case of murder of person the guilty can be convicted and executed as a murderer only if he actually succeeds and murders the victim, so too in this case, the witnesses are only executed if they succeed and have the accused wrongfully executed. The Sadducees learn this from the verse that states “A life for a life”. The witnesses have their lives taken away only if the accused already lost his life.
The Sages, who assumedly are Pharisees, the predecessors of the Rabbis of the Mishnah, state that the perjurers are executed once the verdict has been delivered, meaning the wrongful verdict that they attempted to impose upon the accused. If their testimony is contradicted beforehand then they are not executed because they were not even successful in getting a verdict pronounced against the accused. The Sages arrive at this conclusion by finding the middle ground between two seemingly contradictory verses. Verse 19 says that “you shall do to him as he schemed to do to his fellow” which sounds like “his fellow” is still alive when the perjurers are executed. From this verse alone we might have concluded that the perjuring witnesses are executed as soon as their testimony is found to be false, even if the accused has not been convicted. However, verse 21, “a life for a life” seems to imply that the perjurers are executed only if the accused actually loses his life, as the Sadducees said. The middle ground is that the perjurers are not executed immediately after they give their testimony (and they are found to be perjuring themselves) nor must the accused have been actually executed for the perjurers to be executed. Rather they are executed if the trial was completed, the accused found guilty and then the witnesses proven to be perjurers.