I just wonder where the fire started. The door at the top of the ladder leading to the flight deck is normally kept closed and is designed to keep out smoke from the main deck cargo area, but that would be of little use if the fire was within the upper deck area, like a galley fire, or in the forward area of the main deck and burnt through the upper deck floor or back wall.
Let us hope the investigators have enough evidence left to positively identify the cause and make sure it never happens again.