Numbers 35:15-19

These six cities shall be a refuge for the sons of Israel, for the stranger, and for the foreign resident among them; so that anyone who kills a person unintentionally may flee there.

‘But if he struck him with an iron object, so that he died, he is a murderer; the murderer must be put to death.

And if he struck him with a stone in the hand, by which he would die, and as a result he did die, he is a murderer; the murderer must be put to death.

Or if he struck him with a wooden object in the hand, by which he would die, and as a result he did die, he is a murderer; the murderer must be put to death.

The blood avenger himself shall put the murderer to death; he himself shall put him to death when he meets him.