Comment by eudamoniac

Well first of all if thirty books disappear in one day, that's probably an inorganic usage. If none of them ever reappear, that's another indicator. And then if the person you see taking thirty books is dressed in rags with a shopping cart, you can be pretty confident.

Or maybe OP just means that none of them ever return; it's supposed to be a LF Library after all, not a LF bookshelf.