Мидраш к Бамидбар 35:17
וְאִ֡ם בְּאֶ֣בֶן יָד֩ אֲשֶׁר־יָמ֨וּת בָּ֥הּ הִכָּ֛הוּ וַיָּמֹ֖ת רֹצֵ֣חַֽ ה֑וּא מ֥וֹת יוּמַ֖ת הָרֹצֵֽחַ׃
И если он ударил его камнем в руке, из-за чего человек может умереть, и он умер, он - убийца; убийца, несомненно, будет предан смерти.
Mekhilta d'Rabbi Yishmael
"with stone or fist": I might think that he is liable (only if he strikes) with these, but otherwise he is not liable; it is, therefore, written (Numbers 35:17) "And if with a hand-stone (i.e., a stone the size of a full hand) (whereby he can die he strike him"). He is not liable until he strikes him with something that has the potential to kill and in a locus which is critical to life.
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