(ו) אֵין הָעֵדִים זוֹמְמִין נֶהֱרָגִין, עַד שֶׁיִּגָּמֵר הַדִּין, שֶׁהֲרֵי הַצְּדוֹקִין אוֹמְרִים, עַד שֶׁיֵּהָרֵג, שֶׁנֶּאֱמַר נֶפֶשׁ תַּחַת נָפֶשׁ. אָמְרוּ לָהֶם חֲכָמִים, וַהֲלֹא כְבָר נֶאֱמַר (דברים יט) וַעֲשִׂיתֶם לוֹ כַּאֲשֶׁר זָמַם לַעֲשׂוֹת לְאָחִיו, וַהֲרֵי אָחִיו קַיָּם. וְאִם כֵּן לָמָּה נֶאֱמַר נֶפֶשׁ תַּחַת נָפֶשׁ, יָכוֹל מִשָּׁעָה שֶׁקִּבְּלוּ עֵדוּתָן יֵהָרֵגוּ, תַּלְמוּד לוֹמַר, נֶפֶשׁ תַּחַת נָפֶשׁ, הָא אֵינָן נֶהֱרָגִין עַד שֶׁיִּגָּמֵר הַדִּין:

(6) 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.

(יח) וְדָרְשׁ֥וּ הַשֹּׁפְטִ֖ים הֵיטֵ֑ב וְהִנֵּ֤ה עֵֽד־שֶׁ֙קֶר֙ הָעֵ֔ד שֶׁ֖קֶר עָנָ֥ה בְאָחִֽיו׃ (יט) וַעֲשִׂ֣יתֶם ל֔וֹ כַּאֲשֶׁ֥ר זָמַ֖ם לַעֲשׂ֣וֹת לְאָחִ֑יו וּבִֽעַרְתָּ֥ הָרָ֖ע מִקִּרְבֶּֽךָ׃ (כ) וְהַנִּשְׁאָרִ֖ים יִשְׁמְע֣וּ וְיִרָ֑אוּ וְלֹֽא־יֹסִ֨פוּ לַעֲשׂ֜וֹת ע֗וֹד כַּדָּבָ֥ר הָרָ֛ע הַזֶּ֖ה בְּקִרְבֶּֽךָ׃ (כא) וְלֹ֥א תָח֖וֹס עֵינֶ֑ךָ נֶ֣פֶשׁ בְּנֶ֗פֶשׁ עַ֤יִן בְּעַ֙יִן֙ שֵׁ֣ן בְּשֵׁ֔ן יָ֥ד בְּיָ֖ד רֶ֥גֶל בְּרָֽגֶל׃ (ס)
(18) and the magistrates shall make a thorough investigation. If the man who testified is a false witness, if he has testified falsely against his fellow, (19) you shall do to him as he schemed to do to his fellow. Thus you will sweep out evil from your midst; (20) others will hear and be afraid, and such evil things will not again be done in your midst. (21) Nor must you show pity: life for life, eye for eye, tooth for tooth, hand for hand, foot for foot.
אמרו להם חכמים והלא כבר נאמר (דברים יט, יט) ועשיתם לו כאשר זמם לעשות לאחיו והרי אחיו קיים ואם כן למה נאמר נפש תחת נפש יכול משעה שקבלו עדותן יהרגו תלמוד לומר נפש תחת נפש הא אינן נהרגין עד שיגמר הדין:
The Rabbis said to the Sadducees: But wasn’t it already stated: “And you shall do to him as he conspired to do to his brother” (Deuteronomy 19:19), and this latter verse indicates that his accused brother is alive? And if so, why is it stated: “A life for a life”? One might have thought that if they are rendered conspiring witnesses from the moment the judges accepted their testimony in court, they will be executed, even though no verdict was concluded. Therefore, the verse states: “A life for a life,” teaching that they are executed only if they are rendered conspiring witnesses after the verdict of the accused will be concluded, from the moment that the court is on the verge of taking his life.