How To: Get access to the mages' cache in Ostagar in Dragon Age: Origins

Is that locked chest next to the Tranquil mage in Ostagar driving you crazy? There's a way to unlock it! The man with the key is currently dangling in a cage elsewhere in camp. Convince the guard to share his dinner with the prisoner, and he'll give you the key. Sneak back after nightfall, and it's all yours!