Sotah 102

2:
We have seen that the initial impetus in the matter of the unknown killer must come from the local Bet Din. A corpse has been found and, in the words of the Torah [Deuteronomy 21:1] "it isn't known who has struck him", the matter is reported to a Bet Din which summons elders from Jerusalem to carefully measure the distance which separates the deceased from the settlement nearest to the place where he was struck down – the settlement from which, presumably, the deceased issued forth on his last journey.

3:
The Bet Din must satisfy itself of one thing concerning the body which has been discovered in order to set the machinery in motion: it must ascertain that the identity of the murderer really is not known. For if the culprit is identifiable (even if not yet apprehended) then the major circumstance of the Torah has not been met. If there was an identifiable murderer it is known upon whom the blood-guilt rests. Every effort should be made to apprehend the criminal and bring him to trial, but the blood-guilt rests upon him – whoever he may be – and not upon the general population.

4:
I have already mentioned the suggestion of one commentator (Tosfot Yom-Tov – Rabbi Yom-Tov Lippmann Heller) that all the fuss and bother connected with the activity of the Bet Din in this matter is designed to bring attention to the fact that someone was killed and exactly where they were killed: hopefully, this attention will jog someone's memory and it can then transpire that the murder was not unwitnessed. Therefore, as Rambam points out, it would not be surprising if during all this flurry of activity one witness or more were to come forward.

5:
The Torah specifies that this whole ceremony is to take place only 'when it is not known who struck' the deceased; from this language the sages deducted that if it is ascertainable who the murderer was the ceremony is not to take place, even if that knowledge comes from only one witness. (We have already seen in our study of 6:4 that in some cases the Torah seems to accept the testimony of a sole witness – and even of a witness who would otherwise be considered disqualified.)

6:
If two witnesses come forward with contradictory testimony concerning the possibility of identifying the murderer the culprit is still unidentified and the ceremony must take place. (This is on the assumption that the witnesses present themselves before the Bet Din at the same time; if the testimony of a sole witness – qualified or unqualified – has already been accepted and later a contradictory witness comes before the court the second testimony does not negate the previous testimony which has already been accepted. See our explanations on 6:4.)

7:
However, it is clear that if three witnesses present themselves simultaneously before the Bet Din, two of whom contradict the one who claims to have witnessed the murder, then the murderer is still unidentified. If the opposite is the case – two witnesses claim to have witnessed the murder and only one contradicts them – the ceremony of the 'decapitated calf' is not performed because the murderer is identifiable (even if as yet unidentified or not yet apprehended).

9:5 would seem to strengthen the symbolism of the 'decapitated calf'. It must be a heifer that has not been worked with – it is in place of the victim, who has tragically been killed before he/she accomplished all that he/she could have. The Rabbis took the description of the decapitation site ("unplowed and unsown") as a prescription for how we should treat the site afterwards, rather than as a condition for what kind of site could be chosen – thus, they require us to keep reminding ourselves that, just as we may not grow plants here, nothing will ever grow out of the deceased victim.