וַֽעֲשִׂ֣יתֶם ל֔וֹ כַּֽאֲשֶׁ֥ר זָמַ֖ם לַֽעֲשׂ֣וֹת לְאָחִ֑יו וּבִֽעַרְתָּ֥ הָרָ֖ע מִקִּרְבֶּֽךָ:
then you shall do to him as he plotted to do to his brother, and you shall [thus] abolish evil from among you.
as he plotted: But not as he did. From here [our Rabbis] said that if the first set of witnesses [before being proven false,] already killed the defendant [by their testimony], they are not to be put to death.
What is strange is that the Mishna [Makos 5b] says something different.
אמרו להם חכמים, והלא כבר נאמר (דברים יט) ועשיתם לו כאשר זמם לעשות לאחיו, והרי אחיו קיים.
Why doesn't Rashi quote the Mishna properly?