Isaac's brows furrow together as he listens to Addie's explanation. There are just so many things wrong with this picture -- not necessarily the tale Addie is telling -- but the relationship and power struggle between her and Lansing. What must it be like to be so afraid of your spous finding out the truth about you that you need to hide it and destroy the evidence?
Though his interrogation is supposed to focus around Addie's alleged connection to the Dog King and any information about the Capitol she might have been passing along, the first question out of his mouth is, "Did you ever feel unsafe with your husband? Did he ever threaten you or intimidate you or--hurt you?" He and Addie have known each other for a long time here at the Capitol, and though he's always known what a pecuilar man her husband is, Isaac never imagined that would be turned against his wife. Isaac doesn't want to believe that their marriage could be toxic enough that she would need an out, but if her deception has been rooted in maintaining her safety, that might explain her actions better.
Pressing forward, he asks, "If you didn't know of your brother's title, why the fear of Rob finding out?" He supposes that even the title of 'Cop Killer' is a good enough reason, but there's bound to be plenty of criminals in the city whose crimes proceeded the zombie apocalypse. With the limited manpower, there is just no way that the DoJ can go after every single criminal in Austin.