Quote Originally Posted by Valda View Post
Question - why "арестовали"?

Shouldn't we use the past participle short form "арестован" meaning "was arrested"?

You used plural, and past. While the sentence is past particple, singular male.
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".