[Smokin' Joe]

A ground penetrating radar survey would likely have revealed the presence of graves, occupied and otherwise, to be compared with the records of exhumations done previously. Any 'hits' unaccounted for could have been checked on site.

IMHO, this is just poor planning.

I find it amazing that a school administrator was surprised by the find...well, maybe not.

[AirForceMom]

I don't think they wanted to advertise the fact that they probably would find graves before they started. Might make some people object. Better to "find" them by accident.