Deuteronomy 17:6-7
[6]On the evidence of two witnesses or three witnesses, he who is to die shall be put to death; he shall not be put to death on the evidence of one witness. [7]The hand of the witnesses shall be first against him to put him to death, and afterward the hand of all the people. So you shall purge the evil from your midst.
It is said that the hand of the witnesses were the first to act against the offender in this case
What was the significance of this?
I found an interesting suggestion by Gill's exposition that it was to test the witnesses to see if they are really convinced that the suspect is guilty of his crime, for if they would be liars or plain unconvinced that he is guilty they wouldn't have the gall to murder him like that:
they were to cast the first stone at him, which would be a further trial and confirmation of their testimony; for if they readily and without reluctance first began the stoning of the idolater, it would not only show their zeal for the honour of the divine Being, but an unconsciousness of guilt in their testimony, and be an encouragement to others to proceed with safety
