Dear Rabbi Kornfeld,
I was always under the impression that the word "Rotze'ach" is a murderer whereas "Horeg" refers to one who kills (whether by accident or intent). We would not refer to one who kills someone in a road accident that he is a ROTZEACH.
Yet the Gemoro in Sanhedrin 35b refers to the killing of one condemned by Beis Din as RETZICHA.
I would appreciate hearing your comment.
Excellent point, the wording bothered me as well. As for your thesis that "Ratzach" always refers to the intentional manslaughter of an innocent man, so indeed writes the RASHBAM (on "Lo Sirtzach," Shmos 20:12; this might have been learned from the wording of the Pasuk in Bamidbar 35:21. The interesting background to the Rashbam's comment seems to have been a missionary argument that the verse "Hash-m Memis u'Mechayeh," Devarim 32:39, is referring to their god, who was killed unjustly and according to their claim will return. The Rashbam argued that it does not say "Ratzach" but "Memis," which refers to the just taking of lives that Hash-m practices daily, on each person when their time is due.). This is probably why the word "Ratzach" is never used with reference to the slaughter of an animal; it is a reference to the Aveirah and not just to the act of killing.
The Rashbam challenges this definition from the fact that the Torah uses the word "Ratzach" to describe an unintentional killer (in the Parshiyos of Arei Miklat, see Bamidbar 35:11,25 etc. and Devarim 4:42). His answer is somewhat forced (and is rejected outright by Werthheimer in his Shemos Nirdafim, p. 224). Another possible answer is that a Rotze'ach b'Shogeg is punished with Galus only because his act was done in a manner that could have been prevented (i.e. not "Karov l'Ones" or Derech Aliyah). The Torah calls him a Rotze'ach to allude to this point. Note, however, that the verse also uses the word "v'Ratzach" to describe the Goel ha'Dam killing the Rotze'ach (Bamidbar 35:27), which according to some opinions in Makos is a Mitzvah.
I do not know why the Gemara uses the term Retzichah in our Sugya, or in other Sugyas when referring to Misas Beis Din (see for example She'iltos to Parashas Vayechi #34, "b'Yom she'Atah Rotzcho Atah Kovro"). If "Retzichah" is not limited to the killing of the *innocent* (as the Rashbam writes), but to any *intentional* killing, it would indeed be an appropriate term to describe Misas Beis Din.