Midrash su Deuteronomio 20:15

(Exodus 23:7) "and a clean one and a righteous one you shall not kill": If one testified against another that he worshipped the sun, and another, that he worshipped the moon, I might think that they combine (to constitute the necessary two witnesses) to incriminate him. It is, therefore, written "and a righteous one (i.e., 'technically' righteous) you shall not kill." If they saw him pursuing another to kill him, the knife in his hand, and they said to him: Be it known to you that he is a son of the covenant, and the Torah writes "and a clean one and a righteous one you shall not kill," and (Genesis 9:6) "The spiller of the blood of a man, by man shall his blood be spilled," and he said "I know, and even so!" And the witnesses averted their eyes (for a moment and afterwards they found him (the victim) in the death throes, the knife dripping blood in the hand of the murderer — I might think that he is liable (to execution); it is, therefore, written "and a clean one and a righteous one you shall not kill." Once Shimon b. Shetach had a (single) scheming witness (zomem) executed, whereupon Yehudah b. Tabbai said to him "May I (not) see the consolation if you did not spill innocent blood! For the Torah writes "Kill by witnesses, "Kill scheming witnesses" — Just as witnesses — two, so, scheming witnesses — two (must be killed)! Once Yehudah b. Tabbai entered a ruin, where he found a man in his death throes, the knife dripping blood in the hand of the murderer — to whom he said "May '—' come upon me if neither I nor you killed him; but what can I do (to you) when the Torah has written (Devarim 20:15) 'By word of two witnesses shall a thing be established!' But the Omniscient One will exact punishment of that man (i.e., 'you')." He had hardly finished speaking before a snake bit him and he died. Variantly: "and a clean one and a righteous one you shall not kill": If one left beth-din incriminated, and afterwards some defense were found for him, I might think that he remains incriminated; it is, therefore, written "and a clean one and a righteous one do not kill." Variantly: If one left beth-din vindicated and afterwards some incrimination were found against him, I might think that he is returned for incrimination; it is, therefore, written "and a clean one you shall not kill." (I might think that in such an instance) just as he left your beth-din vindicated, so, he will leave My beth-din (vindicated); it is, therefore, written (Ibid.) "for I will not vindicate the evildoer." Now does this not follow a fortiori, viz.: If re the (lesser) measure (of the Holy One), that of punishment, it is written "for I will not vindicate the evildoer," how much more so in (implementation of) the greater measure, that of good, (will He bestow it to its outermost limits!)

(Devarim 20:15) "Thus shall you do to all the cities that are distant": The distant ones (i.e., those not of the seven nations) are subsumed in this law (to spare the women and children), but those that are near (i.e., the seven nations) are not subsumed in this law.