Commentary for Deuteronomy 21:7

ידינו לא שפכה [AND THEY SHALL ANSWER AND SAY,] OUR HANDS HAVE NOT SHED [THIS BLOOD] — But would it enter anyone’s mind that the elders of the court are suspect of blood-shedding?! But the meaning of the declaration is: We never saw him and knowingly let him depart without food or escort (if we had seen him we would not have let him depart without these) (Sifrei Devarim 210:2; Sotah 45b). The priests thereupon say (next verse): כפר לעמך ישראל FORGIVE UNTO THY PEOPLE ISRAEL.

ידינו לא שפכו את הדם הזה, we have not left a stone unturned in (making public) locating the murderer in the land.

The kohanim then say, “Forgive your people Yisroel.” Otherwise, for what purpose are the kohanim [coming] here? [The presence of elders] is understandable for it is written, “And all the elders of that town [those near the corpse, etc. will wash their hands.”] But why are the kohanim needed? They [are the ones who] recite, “Forgive your people Yisroel.”