Hi rav Kornfeld, a question on the first mishna. If we only punish the edim zomemim after nigmar hadin, but before the punishment is carried out, how is there ever a punishment for the edim in Ben gerusha/chalutza? In that case as soon as there is nigmar hadin, the accused changes status to ben gerusha/chalutza. So we shouldn't be able to punish at all, since there's no time in between. "kaasher zamam ve lo kaasher osa"
Thank you
1) See Rambam, Hilchos Edus 20:2, who writes that it is only if the accused was killed that we then say that the Edim Zomemim cannot be killed, but if the accused received Malkus and then the Edim are found to be Zomemim, the Edim also receive Malkus. Similarly, if the accused was forced to pay money and then the Edim were found to be Zomemim, the Edim have to pay up.
The Radbaz, on the Rambam there, writes that this is derived from the verse, "And you shall do to him what he planned to do to his brother," which implies that his brother is still alive (as the Mishnah 5b states). This is why, if the accused has already been killed, the Edim are no longer killed. However, if the accused only received Malkus he is still alive, so the Edim can also receive the punishment they planned for the accused. The Radbaz concludes that this matter requires further study.
At any rate, according to the Radbaz, since in the case of the Ben Gerushah the accused is still alive, the Derashah of "Ka'asher Zamam v'Lo Ka'asher Asah" does not apply, so it is still possible to punish the Edim of Ben Gerushah/Chalutzah.
2) The Kesef Mishneh gives another explanation for why "Ka'asher Zamam v'lo Ka'asher Asah" applies only if the accused was killed. This is because the crime of the false witnesses was so great that it is not fitting to give them the capital punishment of Beis Din, since this gives them an atonement. It is better to leave them to be judged after their death with the more severe punishments in Shamayim.
3) I found that the Aruch la'Ner (5b, on the Gemara "Chayavei Galiyos Minayin") gives another reason for why "Ka'asher Zamam v'Lo Ka'asher Asah" does not apply to testimony about a Ben Gerushah/Chalutzah. This is because saying that a supposed Kohen is a Ben Gerushah is testimony both on the past and on the future. Any children born to him before the testimony are disqualified from serving as Kohanim, and any children born afterwards are also disqualified. Therefore, it is not "Kasher Asah" because they have not yet finished doing what they plotted.
The Aruch la'Ner writes that this is similar to witnesses who were made Zomemin after their victims had paid some of the money which the witnesses falsely testified that they are liable to pay, but before they have finished paying it all. For the money that they have not yet paid, "v'Lo Ka'asher Asah" would not apply, because the effects of their actions have not yet finished.
4) I also saw in Tosfos Bava Kama (4b) that the Riva explains that "Ka'asher Zamam v'Lo Ka'asher Asah" does not apply when the Edim falsely made their victims pay money. This is because the money can be returned (so it is not considered that the Zomemim have done anything, since it is possible to undo what they did by their act of returning the money).
The Mesivta edition (Makos 2a, Yalkut Bi'urim page 5) cites ha'Me'ir la'Olam (1:2) and Mishkan ha'Edus (Sha'ar 8, Perek 4) who write that the same logic applies to making a Ben Gerushah, since this is reversible when the Beis Din announces that the disqualified Kohen has been re-instated. "Ka'asher Asah" applies only when the witnesses did something irreversible.
Kesivah v'Chasimah Tovah,
Dovid Bloom