The third pair of graves are said to be in underground vaults and corridors which, for reasons which have spurred theorists on, are blocked. Their presence, therefore, can only be wondered at.
No one knows where, or when, the entrance to the underground corridors were bricked up; there's no evidence of it during the British period from 1803 to 1947. Neither is there any record of it during the 18th century when the Jats took over from the [G 15 / Moguls].
If indeed the third graves exist in a set of underground vaults, they may have been filled in by Aurangzeb in the 1650s because of cracks caused by the tremendous weight of the structure above.
The opposing view says no support to the structure would have been given by filling in the vaults and that, although it agrees that Mumtaz Mahal's grave is somewhere down there, Shah Jahan filled the vaults in for secret reasons of his own.
