But still, let his blood be spilled from other limbs (and not through "the sword" [i.e., decapitation])! It is, therefore, written (in respect to eglah arufah [the "heifer of the broken neck"], Devarim 21:4) "And they shall break there (with a hatchet) the neck of the heifer in the river-bed … (9) and you shall remove the innocent blood from your midst." All spillers of blood are likened to eglah arufah — Just as eglah arufah, by decapitation, so, all spillers of blood by decapitation. We have heard of the punishment. Whence (is derived) the exhortation? (Exodus 20:13) "Thou shalt not kill."
Still, Let His Blood Be Spilled from Other Limbs
Mekhilta Tractate Nezikin 4:10