Numbers 35:16-24, 30-31

But if he smote him with an instrument of iron, so that he died, he is a murderer: the murderer shall surely be put to death. And if he smote him with a stone in the hand, whereby a man may die, and he died, he is a murderer: the murderer shall surely be put to death. Or if he smote him with a weapon of wood in the hand, whereby a man may die, and he died, he is a murderer: the murderer shall surely be put to death. The avenger of blood shall himself put the murderer to death: when he meeteth him, he shall put him to death. And if he thrust him of hatred, or hurled at him, lying in wait, so that he died, or in enmity smote him with his hand, so that he died; he that smote him shall surely be put to death; he is a murderer: the avenger of blood shall put the murderer to death, when he meeteth him. But if he thrust him suddenly without enmity, or hurled upon him anything without lying in wait, or with any stone, whereby a man may die, seeing him not, and cast it upon him, so that he died, and he was not his enemy, neither sought his harm; then the congregation shall judge between the smiter and the avenger of blood according to these ordinances

Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die. Moreover ye shall take no ransom for the life of a murderer, that is guilty of death; but he shall surely be put to death.