כִּי־יִמָּצֵא חָלָל בָּאֲדָמָה נֹפֵל בַּשָּׂדֶה לֹא נוֹדַע מִי הִכָּהוּ׃

If  a slain person is found  lying in the field, and it is not known who injured him;

וְהוֹרִדוּ זִקְנֵי הָעִיר הַהִוא אֶת־הָעֶגְלָה אֶל־נַחַל אֵיתָן

the elders of that city shall bring down a  heifer (young cow)
to a rough valley

וְעָרְפוּ־שָׁם אֶת־הָעֶגְלָה ׃
וְכֹל זִקְנֵי הָעִיר הַהִוא הַקְּרֹבִים אֶל־הֶחָלָל
יִרְחֲצוּ אֶת־יְדֵיהֶם עַל־הָעֶגְלָה הָעֲרוּפָה בַנָּחַל׃

And then they , shall slay its neck there .
and wash their hands over the slain heifer

And they shall speak and say:
'Our hands have not shed this blood,
neither have our eyes seen it.

כַּפֵּר לְעַמְּךָ יִשְׂרָאֵל
אֲשֶׁר־פָּדִיתָ יְהוָה
וְאַל ־ִּתֵּן
דָּם נָקִי בְּקֶרֶב עַמְּךָ יִשְׂרָאֵל
וְנִכַּפֵּר לָהֶם הַדָּם׃

דברים כא' א'

Forgive,  your  people Israel,
whom you  hast redeemed,
and do not let  not innocent blood
remain  the midst of them
And the blood shall be
forgiven them.

Deuteronomy 21:1