I'm trying to find the last Spirit of Arkham in Batman, Arkham Asylum, but I am totally stumped. I have otherwise completed the game 100% (including the challenges) and this seems to be the last thing left to do.

It seems like I am supposed to find a person and from the previous clues, I am fairly sure that person is Warden Sharp. However, I have not seen him in ages and I have no idea where he might be. He's not in his office. I feel like I have spent several hours now combing every inch of the island and all of the buildings, spoken to every living person I can find, but no luck.

I would very much prefer a subtle hint, rather than a heavy spoiler, just to set me in the right direction. I have a couple of questions in particular that I would really like answers to, so perhaps we could just start with these for now?:

1. What is it I actually need to do, once I find the correct person? Do I just need to talk to them, or is there more required than that?

2. Am I correct that it is Warden Sharp? If so, is there any subtle clue you can give me as to where I can find him?

Thanks in advance (again, please no heavy spoilers)!