Deuteronomy 21:9

So you shall purge the guilt of innocent blood from your midst , when you do what is right in the sight of the Lord .

and you will have purged from yourselves the guilt of shedding innocent blood, since you have done what is right in the eyes of the Lord.

So shalt thou put away the guilt of innocent blood from among you, when thou shalt do that which is right in the sight of the Lord.