A Freudian slip by the mayor? Could some of SLC's elite old Mormon guys have visited that basement for extracurricular activies? Why, in a house as large as that, would there even BE a bedroom in the basement? Or is it a combination disaster-shelter next to the storeroom with the one year's supply of food, etc.?
And if the girls sometimes slept in the basement (BTW, not a very safe thing to do)--how would the abductor know enough to go to the turret room the night of the kidnapping? A lucky guess?