To build the WTC, the 17 or so acres that it occupies was dug out to create something they call "the bathtub" which goes more than seven stories below the ground level--apparently, even the debris from the two towers not enough to fill it--at any rate, there seem to have been huge bank vaults in the lower levels, which still contain billions, if not hundreds of billions of dollars worth of gold bullion and jewels. They would hardly want to leave that buried with the dead.