Some conditions must be met, from the ethical perspective of systems of thought that are compatible with libertartianism, natural rights, or classical liberalism, which are all sibling world views.
Let’s stipulate some actual evil in play: the first condition must be the actual, bona fide, demonstrable beyond reasonable doubt guilt of the dictator. Has this person initiated aggression resulting in unjust death, grand loss, or abuse of the rights and prerogatives of a free people?