Комментарий к Дварим 21:9

ואתה תבער BUT THOU SHALT PUT AWAY [THE GUILT OF INNOCENT BLOOD FROM AMONG YOU] — This teaches that if the murderer is found after the heifer’s neck was broken he must nevertheless be put to death, — and this is what Scripture describes as הישר בעיני ה׳ RIGHT IN THE EYES OF THE LORD (cf. Sotah 47b; Ketubot 37b and Tosafot on Ketubot 37b:16.1 ואח"כ נמצא ההורג).

ואתה תבער, when you are aware of someone’s guilt it is up to you to sentence the party and to carry out the sentence and not to rely on heaven to intervene. When you are unaware of the identity of the guilty party, and you have made exhaustive attempts to find him without success, you may rest assured that G’d Himself will take care of the problem.

ואתה תבער הדם הנקי, “You are to remove innocent blood;” Ibn Ezra adds the word עונש, “guilt,” which Moses did nor spell out here. Such guilt existed as in the Holy Land, especially, innocent blood is not to be shed, G’d does not tolerate this for long. By participating in the procedure of eglah arufah one fulfils a positive commandment wiping out the guilt of murder.