הוֹצֵ֣א אֶת־הַֽמְקַלֵּ֗ל אֶל־מִחוּץ֙ לַֽמַּחֲנֶ֔ה וְסָמְכ֧וּ כָֽל־הַשֹּׁמְעִ֛ים אֶת־יְדֵיהֶ֖ם עַל־רֹאשׁ֑וֹ וְרָגְמ֥וּ אֹת֖וֹ כָּל־הָעֵדָֽה׃
「你要把那咒詛的人帶到營外，叫所有聽見的人都把手按在他的頭上，然後全會眾要用石頭打死他。
Ibn Ezra
all the witnesses will lay their hands… because someone may be stoned only by the testimony of witnesses.
Chizkuni
וסמכו, “and all who heard the curse are to place their hands, etc.;” what was the reason for this procedure which had to be performed on the bodies of all people about to be executed legally? The reason is that when judgment was passed, the witnesses on whose testimony this sentence was based had been forced during the proceedings to literally quote the words used by the blasphemer in doing so. This had made them perform this symbolic act by means of which they transferred any guilt that they had been burdened with through that to the blasphemer before the latter was executed. כל השומעים, “all who had heard it;” seeing that he would be executed by stoning due to their testimony.