I'm not sure what anyone here can tell you that your ANC commissioner couldn't find out, but have you asked these questions at an ANC meeting? Or contacted any DC agency that might actually be able to do something? It sounds like the construction on the house was illegal if he did it himself without permits and that can be reported. Has anyone done that? There's probably tax fraud stuff going on (I mean, paying in cash, seriously?) and possibly zoning issues and licensing issues in terms of running a illegal boarding house or something like that, but those are questions people in your neighborhood need to ask the relevant agencies; there's not much we can do since we don't even know what neighborhood you're talking about.