From: Rabbi Moshe Sofer
To: Rabbi Nosson Eliyahu
The Chasam Sofer rejects a proposed proof for the Rambam's ruling that eidim zomemim receive lashes even after their victim has already been lashed. He instead resolves the Rambam by applying the Maggid Mishneh's principle that a kal vachomer can impose malkos even when punishment cannot be derived from direct logic alone, since ein onshin min hadin applies only to capital punishment and not to lashes. This explains why eidim zomemim in malkos cases still receive lashes after the punishment was carried out, while eidim zomemim in capital cases are not executed.
Source: Shu"t Chasam Sofer CM §32