We continue with the chapter of Mishnayos in Maseches Sotah. We learned that the eglah arufah is decapitated when it is not known who the murderer is, and the Mishnah before us discusses a case in which there is a contradiction between the testimonies as to whether the murderer is known or not.
Contradicted testimony, one witness against another:
The words of the Mishnah: "Ed echad omer: ra'isi es ha'horeg, v'ed echad omer: lo ra'isa" - one witness testifies that he saw the murderer, and the second responds that at that very moment when his fellow claims to have seen, he was together with him at the spot, and he certainly saw nothing.
And likewise: "Ishah omeres: ra'isi, v'ishah omeres: lo ra'is" - there is no difference between a valid witness and a woman, who is not valid for testimony in other areas of law; regarding eglah arufah she is valid to testify.
Since the testimonies contradict one another, we have no way to clarify the facts and know who told the truth, and the matter remains in the realm of doubt. Therefore the calf is decapitated, since the doubt stands in place.
Those who come one after the other - the Gemara's clarification:
The Gemara clarifies that this halachah was stated specifically when the two witnesses come at the same time, for then neither one is more believed than the other. But if they came one after the other, the Torah believes the first one who came. For it says regarding eglah arufah: "lo noda mi hikahu" - that there is no person in the world who knows who the killer is, and from here we learn that even if a single person knows, this is not considered a doubt and the law does not apply. It emerges that the first witness who came and said "I saw the murderer" has the status of two witnesses, and therefore if an additional witness comes afterward and contradicts him, he is not believed.
One witness against two:
"Ed echad omer ra'isi, u'shnayim omrim lo ra'isa - hayu orfin" - two witnesses contradict his words, and consequently the matter reverts to a doubt in which it is not known who killed the victim, and they decapitate the calf.
"Shnayim omrim ra'inu, v'echad omer lahem lo re'isem - lo hayu orfin" - two witnesses testify that they saw the murderer, and one claims against them that he was there at that time and they saw nothing. In this case they do not decapitate the calf, since one person cannot contradict the testimony of two.
In summary: In this Mishnah we learned that when the testimonies are contradicted evenly - a witness against a witness, or a woman against a woman - the matter remains in doubt and the calf is decapitated. The Gemara explained that this law was stated regarding those who come together, but the one who comes first is believed like two witnesses by force of "lo noda mi hikahu." And we also learned the principle that one cannot contradict the words of two: one witness against two - they decapitate; two against one - they do not decapitate.