[@Nevix] I'm thinking he has a very low tolerance for crime. If he catches somebody engaging in criminal activities, of any sort, he'll kill them regardless of their sob stories, and regardless of their position in the world. That to some extent includes vigilantes - vigilantism itself wouldn't be punished, but it's likely associated with other activities which deserve death, and the few for whom that isn't true will probably try to stop him sooner or later, thus necessitating their own deaths for indirectly aiding criminals by halting his progress. In doing this, he believes he can scare the city into compliance and completely eradicate crime within its borders, so long as he sticks around for long enough to oversee the transition.