In Numbers 35:9-34, God told Moses to speak unto the children of Israel and give them laws concerning accidental manslaughter and murder. It really is not up to people to decide how to punish a murderer.
Vs. 16 - And if he smite him with an instrument of iron, so that he die, he is a murderer: the murderer shall surely be put to death.
vs. 17 - And if he smite him with throwing a stone, wherewith he may die, he is a murderer: the murderer shall surely be put to death.
vs. 18 - Or if he smite him with an hand weapon of wood, wherewith he may die, and he die, he is a murderer: the murderer shall surely be put to death.
vs. 30 - Whoso killeth any person, the murderer shall be put to death by the mouth of witnesses...
vs. 31 - Moreover ye shall take no satisfaction for the life of a murderer, which is guilty of death: but he shall be surely put to death.
vs. 33 - So ye shall not pollute the land wherein ye are: for blood it defileth the land: and the land cannot be cleansed of the blood that is shed therein, but by the blood of him that shed it.
Moreover, if the evidence against a murderer is irrefutable, the sentence must be carried out swiftly. Ecclesiastes 8:11 - Because sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil.
It would be our wisdom to obey God.