Why does the Torah add the words "Asher Yamus bah" here and in Pasuk 18?
Rashi #1 (citing Targum Onkelos): With reference to a stone 1 that fills the hand and a wooden object that is sizeable, the Torah is teaching us here that, if Reuven murders Shimon with an object other than metal, he is only Chayav Misah if Beis-Din assess that the object with which he killed is sufficiently large to have caused his death (and if it strikes him on a limb that the stone is liable kill ? Rashi in Mishpatim, Sh'mos, 21:20).
Rambam (Hilchos Rotze'ach 3:2): To teach us tht Beis-Din are obligated to evaluate the murder weapon, and also where it struck the victim [to determine whether or not the blow is capable oF killing].
Rashi: To preclude from the notion that "O be'Even asher Yamus bah" (Sh'mos 21:18) and "ve'Chi Yakeh Ish es Avdo ba'Sheivet" (Ibid. 21:20) are referring to a stone or a stick, irrespective of its size.
Why does the Torah insert the (otherwise superfluous) words "Rotze'ach hu Mos, Yumas ha'Rotze'ach"?
Sifri: To teach us that, if the murderer killed the victim by rolling on him rocks or pillars he is also Chayav.
What are the connotations of "Even Yad"?
Rashi #1: It is a stone that fills the hand. 1
Rashi #2: One is only Chayav on a weapon that is capable of killing, and on a location on the body that would cause him to die.
Ba'al ha'Turim: It implies that "Even Yad" - a regular-size sone - must be evaluated, but not Even ha'Melech (the king's weight - which is large stone) 3 which does not require evaluation, since it is certain from the outset that it can kill.
Refer to 35:17:152:1 & 2.
Divrei David: The strength of the one who threw it.
See Shmuel 2, 14:26.
QUESTIONS ON RASHI
Rashi writes that "Even Yad" is a stone that fills the hand. But we already know from "Asher Yamus bah" that it must be able to kill?
Gur Aryeh: If the murder weapon sometimes kills and sometimes does not, we cannot kill the murderer. A stone that fills the hand is always able to kill. 1
Perhaps a stone that fills the hand must be evaluated, but anything bigger than that certainly kills, and need not be evaluated. Refer to 35:17:151:3. Or, a stone that fills and is thrown by hand must be evaluated, but a rock thrown via a slingshot need not be evaluated (since it can certainly kill) PF.
It is astounding to say that such a rock always kills. Surely it need not kill if it is thrown softly, or if it landed not on his torso or if it just nicked his skin! One who must be stoned, if he did not die from the fall, they dropped a giant rock, that needs two people to carry it, on him. If that does not kill him, everyone stones him? Indeed, it always killed him (Sanhedrin 45b). However, if even a stone that fills the hand always kills, all the more so, a giant rock! Was the Mitzvah for everyone to stone him said only if Hashem will do a miracle for a Rasha?! (PF). What the Gur Aryeh probably means is that a stone that fills the hand is always fit to kill - provided it falls in a way that kills - Refer to 35:17:151:2. Consequently, since in the current case it killed the victim, it does not require assessment, as a smaller stone would.
