Is the blood of the aggressor considered spilled in vain, and is retribution (qisas) due from one who kills him in defense of himself and his family, especially after repeated aggression and threats of killing and destruction, and in the absence of a law that protects the victim?

A person should not resort to killing an oppressor unless all means of escaping their oppression have been exhausted. If these means are exhausted and the killing is in self-defense or in defense of one's property, then there is no sin upon him and no retribution. It is permissible for a Muslim to defend himself, his family, and his property against an oppressor, even if it leads to the oppressor's death. This is supported by the hadith: "What do you think if a man comes intending to take my property?" He replied, "Do not give him your property." He asked, "What do you think if he fights me?" He replied, "Fight him." He asked, "What do you think if he kills me?" He replied, "Then you are a martyr." He asked, "What do you think if I kill him?" He replied, "He is in the Hellfire." It is permissible to kill someone who intends to unlawfully seize property, but one should first warn and admonish them.