The death penalty is a cardinal biblical value, which speaks to the Bible's view that innocent human life is sacred. The murderer MUST die. This in contrast to other crimes, for which reparations are allowed. No murderer rich or poor, can escape the ultimate punishment. Man is made in the image of God and so human life has an essence of holiness to it. And there is also the question of justice. The seminal Jewish contribution to the world besides bringing God into it, was to declare justice must be meted out equally regardless of social status. When it comes to murder there can be only one answer.
(Denny Crane: "Sometimes you can only look for answers from God and failing that... and Fox News".) Although it seems an anomaly to some, the fact that conservatives oppose abortion and favor the death penalty, while liberals are on opposite sides, has a basis in the same issue - the value of human life.
The key in the difference between valuing the life of the unborn and not that of a murderer is innocence. Who can be more innocent than an unborn baby? As far as the murderer, the life being valued is that of the victim, not the murderer. To value the killer more than the victim of itself devalues innocence and life.