Numbers 35:16-19

16If, however, anyone strikes a person with an iron object and kills him, he is a murderer; the murderer must surely be put to death. 17Or if anyone has in his hand a stone of deadly size, and he strikes and kills another, he is a murderer; the murderer must surely be put to death. 18If anyone has in his hand a deadly object of wood, and he strikes and kills another, he is a murderer; the murderer must surely be put to death.

19The avenger of blood is to put the murderer to death; when he finds him, he is to kill him.