I would say Jack of Blades owns it. When you go there and get your mother out of the torture chamber the first time, Jack catches you, and part of what he says to your mother is "Did you know he's been crowned Arena Champion? You would have been so proud of him. It must run in the family. That and getting locked up in one of my...charming little cells." Since he says "my cells," that indicates to me that the cells and the prison as a whole are his. Not to mention that when you first get into your cell, the guard who was talking to you says "Oh, and don't try any of that funny Will stuff. It won't work in here. The boss made sure of that." When he says, "the boss," that could only mean the warden or Jack, and it most likely takes some Will powers to disable the Will powers of another, and I doubt the warden can use Will, so it has to be Jack.