Who bears liability for homicide when an authoritative ruler orders a subject to kill another?

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If a ruler orders a man to kill another, and the killer knew that the victim did not deserve death, the retribution (Qisas) falls upon the killer, not the one who ordered it. This is because the killer is not excused for his action. Evidence rests on the Prophet's saying, "There is no obedience to a created being in disobedience to the Creator," and another narration stating, "Whoever among the rulers orders you contrary to obedience to Allah the Almighty, do not obey him." Thus, retribution is incumbent upon the killer, as if a non-ruler had ordered him. However, if the killer did not know the victim did not deserve death, the Qisas falls upon the ruler, not the ordered person, because the ordered person is excused due to the obligation to obey the Imam in matters that are not disobedience, and the apparent assumption is that the Imam orders only what is right.