Opinion within Christendom on capital punishment is mixed. Some Christians believe capital punishment is mandated, while others believe it is merely permitted. In contrast, there are Christians who feel it is biblically prohibited. Those who believe it is prohibited base their argument on an assumption the New Testament reverses the mandate of the Old Testament prophecy which deals with habitual criminals: "Whoever sheds the blood of man, by man shall his blood be shed; for in the image of God has God made man" (Genesis 9:6). However, Romans 13:1-7 implies capital punishment is still permitted under the new covenant. Those who believe capital punishment is permitted but not necessarily required point to the fact that even the Old Testament contains examples of criminal acts that were not punished by death; Cain, Moses, and David all took another man's life, but were not put to death for the killings.
Even though the Bible permits capital punishment, it lays down strict guidelines to keep judgment from being unfair or excessive. Punishment must be commensurate with the crime (Exodus 21:23-25). It must be based on certainty of guilt (Deuteronomy 17:6). It must result from premeditated intent (Numbers 35:22-24). There must be due process; cities of refuge were provided to protect the accused until trial (Numbers 35). Fairness and justice must prevail regardless of wealth or reputation (Exodus 23:6,7). Restraint should be exercised in imposing the death penalty (Ezekiel 33:11).
Deuteronomy 19:21 is sometimes noted as Old Testament support for capital punishment: "Show no pity, life for life, eye for eye, tooth for tooth, hand for hand, foot for foot." But the context in which this statement appears deals with the treatment of proven false witnesses. Under Jewish law, the accusation of two or three witness was all that was needed to convict the accused. The defendant had to prove himself innocent. False witnesses would make a mockery of the system of justice. Once guilt was established, the punishment had to fit the crime, neither exceeding the injury done nor handing down some inconsequential punishment for a serious crime (Exodus 21:12-36, Leviticus 24:17-22).
Both the Old and New Testaments indicate that personal retaliation is not appropriate (Leviticus 19:18; Romans 12:19-13:7). Punishment should be the prerogative of the government/community, not of the individual. No matter how heinous the crime, retaliation just to settle a personal vendetta, is contrary to biblical principles. Proponents of capital punishment give three possible reasons to mandate the ultimate sentence: (1) deterrence of potential offenders who might be inclined to commit a major crime, (2) deterrence of a criminal who if free might repeat the same offense; an executed murderer could not murder again, (3) retribution or repayment to victims or society for losses sustained because of the crime.