What is the ruling on a person who kills a man and a woman while they are in a state of adultery?

Whoever sees a woman committing adultery, and she is not his wife, must rebuke the one doing that, and not speak about it; because it is slander (qadhf) that necessitates the eighty lashes, unless he is the fourth of four witnesses, to testify to the adultery. If he kills them, he is subject to qisas (retaliation). However, if she is his wife, he must perform li'an (mutual imprecation), by testifying four times by Allah that he is among the truthful, and the fifth time that the curse of Allah be upon him if he is among the liars. If the woman testifies four times by Allah that he is among the liars, and the fifth time that the wrath of Allah be upon her if he is among the truthful, they will be separated forever. If she refuses to testify, the prescribed punishment will be carried out against her. If he claims adultery but does not perform li'an, he will be subject to the punishment for qadhf. If he kills them, his statement is not accepted, and he is subject to qisas, unless there is clear evidence (four upright male witnesses) or the heirs of the slain admit it, or he is excused for his action if signs of his truthfulness appear.