Though I don't know Hebrew, I'm told by those who do that the verb in "thou shalt not kill" translates as "thou shalt not commit murder." (Exodus 20:13)
What, then, is "murder"? Does killing someone who has killed qualify?
To the ancient Hebrews (Genesis 9:5-6), the answer was obvious:
An eye for an eye
A tooth for a tooth
A life for a life.
Memorable, poetic language, with a clear moral core: Each human life is to be respected because each human being is made in the image and likeness of God.
But even a bedrock biblical statement like this does not stand outside of time; it must be interpreted. (As my dad used to say, summing up much of the German theology he had studied at Luther Seminary before anyone in America had heard of Derrida, text + context = meaning.) As banal as it is to say it, three thousand years is a long time, and what "a life for a life" means today isn't settled in two seconds merely by saying "Genesis 9:5-6." More than a tautology (life = life) is necessary to contribute meaningfully to today's death penalty debate in America.
To be sure, the Bible is foundational. It's a complicated compendium of books, however, with contrasting viewpoints in dialog with each other. The "a life for a life" statement in Genesis must be evaluated against the words of Jesus, who broke up an execution by saying he who is without sin should cast the first stone. In short, we must use our minds, and our knowledge of contempory culture, to gain insight from the Bible on the question of the death penalty.
So put the "proof-texts" aside and consider the factual settings set forth in the real death penalty cases to be highlighted in Amnesty International's upcoming Death Penalty Awareness Week.