Rabbits don't lay eggs.
In the beginning was the proclamation "whosoever sheds the blood of man, by man shall his blood be shed..." (Gen 9:6) and in the end there was "Father forgive them, they know not what they do" (Luke 23:34). In between is a complex problem left completely unresolved, and too many verses for even the scholar to sift through authoritatively.
The question: Do we have the justification to kill? Capital punishment still exists in Christian societies, and most look to the Law set out by God in the Old Testament. After all, the Old Testament and the New Testament are divided so that the Old Testament deals with societal ethics, and the New with personal ethics. Therefore, though Jesus said to forgive personal offences, the Law and the judges are compelled to destroy those who insult God. Hank Hanegraaff articulates the argument for capital punishment best when he says that it is a "sanctity of life" issue. Those who kill the apex of God's creative energies are not only destroying a human being, they are sending a personal defiance to God, a personal attack against His sacredness. To allow such a rejection of God's Will is to reject God's majesty and a court cannot do that. Such people need to be terminated, if only because an insult to God should not go unpunished.
But there are those who do not agree. The charges brought against Jesus by the Sanhedrin, those that ultimately led to his crucifixion, were of rousing the Jews not just against the Romans, but against God (Mark 14:60-65). The Law passed down from Genesis to punish those who insult God with death was the same justification used to kill his Son on a cross. If one who is without sin can slip through the Law, then there are others too. Those on the other side say that the Law was replaced, through Jesus' subjection to it, by Love and forgiveness.
Still there is no way to know for sure. Jesus did not come to change the government; he specifically tells Satan that when he is tempted in the desert. If that is true, then perhaps the Law still stands and the sanctity of life must still be defended. To the death.