"And for your lifeblood I will require a reckoning: from every beast I will require it and from man. From his fellow man I will require a reckoning for the life of man. Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image" (Genesis 9:5-6).
The death penalty (in case of murder) is not only biblical, but commanded. There is no negotiation in this passage, and God justifies and gives the reason for it on the basis of our creation. It deserves the highest form of punishment.