יַ֣ד הָעֵדִ֞ים תִּֽהְיֶה־בּ֤וֹ בָרִאשֹׁנָה֙ לַהֲמִית֔וֹ וְיַ֥ד כׇּל־הָעָ֖ם בָּאַחֲרֹנָ֑ה וּבִֽעַרְתָּ֥ הָרָ֖ע מִקִּרְבֶּֽךָ׃
Let the hands of the witnesses be the first to put the condemned to death, followed by the hands of the rest of the people. Thus you will sweep out evil from your midst.
Torah Temimah points to Sanhedrin 45b.
יד העדים. אמר שמואל, נקטעה יד העדים פטור, מאי טעמא דבעינן יד העדים תהיה בו וליכא, אבל גידמין דמעיקרא לא, מאי טעמא, דאמר קרא יד העדים – שהיתה כבר.
English: “The hand of the witnesses.” Shmuel said: If the hand of the witnesses was cut off, he is exempt. What is the reason? We require “the hand of the witnesses” to be upon him, and it is not; but if they were already without hands from the outset, that does not exempt him. What is the reason? The verse says “the hand of the witnesses” — the hand that they had previously.
The requirement that the witnesses themselves begin the execution is cross-referenced to the parallel language of “hand” developed in the purification rites of the metzora.
Derash on the verse (cross-reference) — not a formal named middah of the 13. The verse is treated as restating a principle already established elsewhere.
The witnesses who testified must themselves take the first physical role in the execution.