Арестовали - "they arrested" - one way in Russian to use impersonal constructions. "They" means no matter who. Somebody. In English it is also used AFAIK even if not so often as in Russian.
Another way is to say the same "он был арестован" - "he was arrested", but it is a bit bookish, official way.
Again the same construction "где ее держат" - "where they held her".