Parashas Masei · Passuk 35:17 · TT note 2
Chabad.org — English translation + Rashi
Torah Temimah points to Sifrei (TT note on “מוֹת יוּמַת הָרֹצֵחַ”).
English: “The murderer shall surely be put to death” — one might think that because it is written “or with a stone” he is liable only if he killed with a stone; from where [do we know] that if he rolled rocks and pillars upon him and killed him he is liable? Scripture says “he is a murderer; the murderer shall surely be put to death” — in any case.
Expansion of liability beyond a hand-held stone to any stone mass that kills.
Death caused by any form of stone (hand-stone or rolled mass) renders the killer a murderer liable to capital punishment.