This Mishnaic passage records a debate between the Sadducees and Pharisees on the treatment of men who gave false testimony in a capital case. Different interpretations of the biblical law resulted in different judicial rulings.
Scheming witnesses 98 are not executed until a verdict [for death] has been rendered [against the accused]. For the Sadducees say- until [the accused] has been executed, as it is written, “life for life” (Deut. 19-21). The Sages said to them- But it is already written, “you shall do to him as he schemed to do to his fellow” (Deut.19- 19). Thus the accused is still alive! If so, then why is it written, “life for life?” One might have thought that they may be killed from the time that their testimony was heard. [To teach otherwise,] the Torah writes, “life for life” from which one can derive that they may not be executed until a verdict has been rendered.
97. Trans. S. Berrin.
98. The term used refers to a particular type of perjured witnesses. Their testimony has been invalidated since a second pair of witnesses testifies that the first pair of witnesses could not have been present at the scene of the alleged crime because the first witnesses were, in fact, in the presence of these second witnesses elsewhere at that particular time. In a capital case, the punishment of these false witnesses is execution.