Katy and I like to watch psychological thrillers from time to time, but I've noticed a recurring trope that confuses me. It goes like this: Psychopath lives in an outwardly normal looking house, but has a secret passage to a secret murder basement.

Who built this? Am I to believe he excavated the earth, poured the concrete, ran the (usually admittedly shoddy) electrical himself? Did no contractor at any point ever think to themselves: "this doesn't seem right. Perhaps I should alert the authorities?"

Edit: typo