Shoftim 6th Portion Part 2

18 The judges must make a thorough investigation [by cross-examining those who come to discredit the witnesses], and if the witness proves to be a liar [“witness” always connotes two], giving false testimony against a fellow Israelite,

Rashi’s Commentary

The judges must make a thorough investigation concerning the statement of those who assert them (the first witnesses) to be “plotting witnesses,” in that they investigate and crossexamine those who assert them to be “plotting witnesses” by diligent enquiry and scrutiny.

And if the witness proves to be a liar—Wherever עֵד is written, Scripture is speaking of two witnesses (Sanhedrin 30a).

19 then do to the false witness as that witness intended to do [but not “as he did”] to the other party [but not to his sister (in an instance of their testifying that the married daughter of a priest was adulterous, in which instance they receive not the adulteress’ penalty (burning), but the adulterer’s (strangulation)]. You must purge the evil from among you.

Makkot 5a:2

MISHNA: When punishing conspiring witnesses based on the verse: “As that witness conspired to do to the other party” (Deu 19:19), one divides the punishment of money among them, but one does not divide the punishment of lashes among them; each receives thirty-nine lashes. The mishna elaborates: How so? If the witnesses testified about someone that he owes another person two hundred dinars and they were then found to be conspiring witnesses, the witnesses divide the sum among themselves and pay a total of two hundred dinars. But if they testified about someone that he was liable to receive forty lashes and they were then found to be conspiring witnesses, each and every one of the witnesses receives forty lashes.

Makkot 5a:4

Rava said: The reason the punishment of lashes is not divided is that we require fulfillment of the verse: “As that witness conspired to do to the other party” (Deu 19:19), and were the conspiring witness to receive fewer than thirty-nine lashes, the verse would not be fulfilled. The Gemara asks: If so, in the case of money too, one should not divide the sum between them, as each sought to cause the defendant loss of the entire sum. The Gemara answers: Sums of money paid by the witnesses can combine, as the person against whom they testified receives the entire sum that they sought to cause him to lose, but lashes administered to the witnesses cannot combine.