kjv@Genesis:9:5@ And surely your blood of your lives will I require; at the hand of every beast will I require it, and at the hand of man; at the hand of every man's brother will I require the life of man.
kjv@Genesis:9:6@ Whoso sheddeth man's blood, by man shall his blood be shed: for in the image of God made he man.
It is very common throughout civilizations that when a beast takes a man's life that the beast is put down. It is feared that once a beast has a taste for human blood, it will return for more. There is a common wives tale that once a man has crossed the line and struck his wife he will back for more. It is not always true, but true in enough situations that at least in the case of murder there is reason to expect more murder. If there is enough logical concern of human nature justifying capital punishment on civil terms (not just for discouragement to others), add to that it is God's express judgment as well, then just and thorough courts have every right/obligation to insist upon capital punishment for the murderous few.
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3