Numbers 35:27

Him. Custom explained this law, as giving leave to any person to inflict the punishment upon the wandering murderer, though the relation seem only to be specified. (Grotius) --- Some think, that to kill such a person was still criminal in the sight of God. But others believe that, as he had forfeited the privilege of an asylum, by absenting himself from it, (Calmet) the law subjected him to the same rigour with which he might have been treated before he came thither; (ver. 19.; Haydock) and provided proper moderation were observed, and malicious revenge avoided, no guilt would attach to him who executed the implied sentence of death. The Jews observe, that God allows us to revenge another sooner than ourselves, as there is less danger of excess or of delusion. (Calmet)