What if…. blackbeard's intentional has all along been one piece?
and the person/key critical to knowing where one piece is, is in the prison?
The plan is to become a key world govt person to access intel from the marine and now to rob/access this person/key to unlock the location of one piece?
Roger was once in the prison, isn't it. He could very well left something important locked in a place where no one escaped before. This event by luffy would simply become a best opportunity to do this?