Is it Islamically permissible to kill an oppressor who wrongs people, as retribution?

The oppression of people is divided into three categories:

1. Oppression that does not necessitate killing: Such as backbiting (gheebah), tale-bearing (nameemah), and slander (qadhf). In these cases, enjoining good and forbidding evil, and reminding people of Allah, are obligatory. 2. Oppression that necessitates killing: Such as intentional killing without just cause. The perpetrator of such an act is executed by the ruler's judgment if the conditions for retribution (qisas) are met. 3. Oppression through aggression (al-sawlah) against a life, property, or honor: This is repelled by the lightest means first, then the more severe. It is permissible to repel it even if it leads to killing. The aggressor is repelled by anyone whose life, property, or honor is inviolable. Repulsion must be by the lightest means possible, and if not possible, then by the more severe. If escape or avoidance is possible, that becomes obligatory.