Morgan and Citi were involved in the 'gold carry trade'. They leased gold from the Treasury at low interest rates (1% or so), sold it, and then invested the proceeds in gov't bonds. They made the spread and it added up to a lot. A nice business, as long as the price of gold doesn't rise. If goes up to much, they won't be able to cover their short positions, which are huge at this point (greater than the global annual production of gold) and the Treasury doesn't get their gold back.