Commentary for Sanhedrin 5:4
וְאַחַר כָּךְ מַכְנִיסִין אֶת הַשֵּׁנִי וּבוֹדְקִין אוֹתוֹ. אִם נִמְצְאוּ דִבְרֵיהֶם מְכֻוָּנִין, פּוֹתְחִין בִּזְכוּת. אָמַר אֶחָד מִן הָעֵדִים יֶשׁ לִי לְלַמֵּד עָלָיו זְכוּת, אוֹ אֶחָד מִן הַתַּלְמִידִים יֶשׁ לִי לְלַמֵּד עָלָיו חוֹבָה, מְשַׁתְּקִין אוֹתוֹ. אָמַר אֶחָד מִן הַתַּלְמִידִים יֶשׁ לִי לְלַמֵּד עָלָיו זְכוּת, מַעֲלִין אוֹתוֹ וּמוֹשִׁיבִין אוֹתוֹ בֵינֵיהֶן, וְלֹא הָיָה יוֹרֵד מִשָּׁם כָּל הַיּוֹם כֻּלּוֹ. אִם יֵשׁ מַמָּשׁ בִּדְבָרָיו, שׁוֹמְעִין לוֹ. וַאֲפִלּוּ הוּא אוֹמֵר יֶשׁ לִי לְלַמֵּד עַל עַצְמִי זְכוּת, שׁוֹמְעִין לוֹ, וּבִלְבַד שֶׁיֵּשׁ מַמָּשׁ בִּדְבָרָיו:
And then the second one is brought in and he is examined. If their words coincide, [so that they must now deliberate on the matter] they (beth-din) open with "merit." ["If you did not transgress, do not fear."] If one of the witnesses says: "I have something to say in his favor," or one of the disciples: "I have something to say against him," he is silenced. [("I have something to say in his favor":) even in his favor, and, it goes without saying that he is silenced if he (a witness) says: "I have something to say against him," viz. (Numbers 35:30): "And one witness shall not testify" — both for acquittal or for conviction. ("one of the disciples":) sitting before the judges. (If he says:) "I have something to say against him," he is silenced, it being written (Ibid.): "One shall not testify in a man to kill him" — "to kill him he does not testify," but he does testify in his favor.] If one of the disciples said: "I have something to say in his favor, he is brought up (to the judges) and placed among them, and he does not descend thence the entire day, [even if there is no substance to his words; but if there is substance to his words, he never descends thence.] If there is substance to his words, he is heeded. And even if he [the accused] says: "I have something to say in my favor," he is heeded, so long as there be substance to his words.
Bartenura on Mishnah Sanhedrin
English Explanation of Mishnah Sanhedrin
If their words were found to agree together they begin [to examine the evidence] in favor of acquittal.
If one of the witnesses said, “I have something to argue in favor of his acquittal”, or if one of the disciples said, “I have something to argue in favor of his conviction”, they silence him.
If one of the disciples said, “I have something to argue in favor of his acquittal”, they bring him up and set him among them and he does not come down from there all day. If there is anything of substance in his words they listen to him. Even if the accused said, “I have something to argue in favor of my acquittal”, they listen to him, provided that there is substance to his words.
Mishnah four deals with the court procedure after the testimony has been presented.
After the second witness is examined, the judges begin to examine the evidence. They first examine evidence that might lead to the accused person’s acquittal. The witnesses are not allowed to testify again, even if they know testimony that might lead to acquittal. The disciples, those students of the Sages who sat in rows in front of the judges, were not allowed to speak in favor of conviction. If, however, one of the students was able to raise a point in favor of acquittal, he would be promoted to one of the judge’s seats and from there he could say what he has to say. Finally, the accused himself may testify on his own behalf, provided his claim has some substantial basis.