Reference for Sotah 9:7

נִמְצָא הַהוֹרֵג עַד שֶׁלֹּא נֶעֶרְפָה הָעֶגְלָה, תֵּצֵא וְתִרְעֶה בָעֵדֶר. מִשֶּׁנֶּעֶרְפָה הָעֶגְלָה, תִּקָּבֵר בִּמְקוֹמָהּ, שֶׁעַל סָפֵק בָּאתָה מִתְּחִלָּתָהּ, כִּפְּרָה סְפֵקָהּ וְהָלְכָה לָהּ. נֶעֶרְפָה הָעֶגְלָה וְאַחַר כָּךְ נִמְצָא הַהוֹרֵג, הֲרֵי זֶה יֵהָרֵג:

If the murderer was discovered before the heifer’s neck was broken, it goes free and grazes with the herd; But if after the heifer’s neck was broken, it is buried in that place because it came there from the outset in connection with a matter of doubt, and atoned for the doubt which is now gone. If the heifer’s neck was broken and afterwards the murderer is discovered, behold he is executed.

Jastrow