Burgundy wants to know. The book in the library says he's in the Sea Caves. I have a theory that he's the skeleton tied to an anchor. But if that is correct, I seem to have no way of making Shawn know that so he can tell Burgundy.

I don't think that Shawn is supposed to find out. More likely that mystery will be solved in a future game.

Aquino is a plot point for future games. He was originally scheduled to make an appearance in the Catacombs in Rogue to Redemption, but we decided it's more appropriate to save him for a later game in the series. He would have just been another adversary for Shawn, where he can become the major antagonist for another character.