Augustine does not, in the end, hold the slave who kills his master to escape torture to be pardonable before the law -- that is, the moral law of God, not the law of the land, or authority. For Augustine, the slave's desire to be free from his master's torture is in fact an inordinate desire, because, unlike a good person, who can "turn their love away from things that cannot be possessed without the fear of losing them" (7-8), the wicked person is unable to let a desire that all humans have -- that is, to live without fear -- go when it is not possible to possess it, and instead holds an inordinate desire for it.
A justifiable desire is one that a person holds for something that one cannot then lose against one's will, while a blameworthy desire -- an inordinate desire -- is for something that one can lose against one's will (8). In other words, a blameworthy desire is one that is held for something outside of one's control, or ability to achieve. If something cannot be lost against one's will, there is no need to hold an inordinate desire for it, since it cannot be taken from the person, but only given or used up freely. The same argument that is used for the unjustifiability of the slave who kills his master is extended to any number of things that can be taken from someone outside of their control -- "life, liberty, or chastity" (8).
This argument is, then, as follows: the slave has, like all humans, the desire to be free from fear. In the slave's case, however, he desires this more than is justifiable -- he desires it inordinately, because it can be once again taken away from him without his control; that is, he can be placed in the condition of living in fear again by forces outside of his command. The good person, however, would see this, and reject the inordinate desire for freedom that drives the wicked slave to kill his master. The good person realizes the temporal nature of the desire to live without fear, and does not sin in attempting to attain it.