מדרש על סוטה 93:11

(Devarim 21:1) "If there be found a slain one on the earth": "If there be found": and not if there were generally found" — to exclude (its being found) near the border or near a city inhabited mostly by gentiles — where it was stated: When murderers proliferated, the breaking of the heifer's neck was abolished. When R. Elazar b. Dinai came, (otherwise known as Techinah b. Prishah), they began to call him "the son of the murderer."