I don't think that the angel's request is as impossible as both the SI and the commenters are saying. The angel is asking for the SI to repent his theft. Not necessarily say that he wouldn't do the same again. The SI could genuinely regret that said theft was necessary, ask for forgiveness that he had to commit a crime in order to achieve goals that will end up helping other people, without saying that he wouldn't do the same again in identical circumstances. This would actually be consistent with the SI's character, because he does generally feel bad about hurting non-evil people, and avoids it if at all possible.
A similar example could be someone deeply regretting and asking forgiveness for killing someone else in self defense. Even if the person recognizes that they were completely right to kill the other person, and would do the same if faced with the situation again, it wouldn't necessarily change the guilt they feel for ending someone's life, and their desire for the situation to have never happened.