There were a couple of progs on Discovery last night regarding the creation of those memorials and the museum that is underneath in the old basement area. Some of the bigger pieces, including a semi destroyed fire truck belonging to a crew which died to a man in the first tower, had to be lowered down through what will be turned into a sky light. It looked in all regards like it was being given a funeral all of it's own and the event was attended by many firefighters.
The black bar around the squares are where the dead's names have been inscribed. They have been put on in no apparent order unless they knew or worked with others, in which case they have been carved next to each other.
One of the main plumbers who set up the huge pumps that power the waterfall had a mum living on the floor where the first jet crashed.
It was a quite fascinating series of programmes.