Midrash sobre Números 35:29

(Bamidbar 35:29) "And these shall be for you a statute of judgment": to obtain throughout the generations": in Eretz Yisrael and outside of it. (30) "Whoever would kill a soul, by the testimony of witnesses shall he kill the slayer": What is the intent of this? From (19) "The avenger, he shall kill him," I might think that he may kill him in beth-din without witnesses. It is, therefore, written "Whoever would kill a soul, by the testimony of witnesses, etc." He kills him only in beth-din and by witnesses. "and one witness shall not testify against a soul to have him put to death": (but) he can testify towards acquittal. And one witness can testify towards (imposing) an oath. "and one witness": This is a prototype, viz.: Wherever "witness" is written, two are understood, unless "one" is specified. (31) "And you shall not take ransom for the soul of a murderer": What is the intent of this? From (Shemot 21:30) "When ransom is set for him" (one whose ox killed a man), I might think that just as "redemption" is given for those subject to death at the hands of Heaven, so, is it given for those liable to death by man (i.e., beth-din). It is, therefore, written "And you shall not take ransom." R. Yoshiyah says: If one were taken out to be executed and he injured others, he is liable. If others injured him, they are not liable for (injuring) his person, (for he is considered "dead"), but they are liable for (damage to) his property. Whence is this derived? From "And you shall not take ransom," (indicating that he is regarded as "dead.") — But perhaps this obtains even if his verdict has not yet been consummated? It is, therefore, written "who is liable to die." Until his verdict has been consummated, he (i.e., one who injures him) is liable. Once his verdict has been consummated, he is not liable. R. Yonathan says: If one were being taken out to be executed, and another came forward and killed him, he is not liable. Even if his verdict has not yet been consummated? It is, therefore, written "until he is liable to die." Until his verdict has been consummated, he (i.e., one who kills him) is liable. Once his verdict has been consummated, he is not liable.