וְכָל־הָעָם֩ רֹאִ֨ים אֶת־הַקּוֹלֹ֜ת וְאֶת־הַלַּפִּידִ֗ם וְאֵת֙ ק֣וֹל הַשֹּׁפָ֔ר וְאֶת־הָהָ֖ר עָשֵׁ֑ן וַיַּ֤רְא הָעָם֙ וַיָּנֻ֔עוּ וַיַּֽעַמְד֖וּ מֵֽרָחֹֽק׃
And all the people perceived the thunderings, and the lightnings, and the voice of the horn, and the mountain smoking; and when the people saw it, they trembled, and stood afar off.
Sefer HaMitzvot
That He prohibited the judge - not to kill someone clean and innocent. And that is His saying, "You shall not murder" (Exodus 20:15). (See Parashat Yitro; Mishneh Torah, Murderer and the Preservation of Life 1.)