Deuteronomy 21:6

Overview - Deuteronomy 21
The expiation of an uncertain murder.
10 The usage of a captive taken to wife.
15 The first-born is not to be disinherited upon private affection.
18 A rebellious son is to be stoned to death.
22 The malefactor must not hang all night on a tree.
Treasury of Scripture Knowledge

Deuteronomy 21:6  (King James Version)
And all the elders of that city, that are next unto the slain man, shall wash their hands over the heifer that is beheaded in the valley:

wash their hands
Washing the hands was anciently a symbolical action, denoting that the person was innocent of the crime in question.
Job 9:30 ; Psalms 19:12 ; 26:6 Psalms 51:2 Psalms 51:7 Psalms 51:14 73:13 Jeremiah 2:22 ; Matthew 27:24 Matthew 27:25
Hebrews 9:10