Don, was the dead hive full of dead bees? Bees scattered on the ground in front of the entrance? Were the bees ever observed bringing *anything* into the hive?
Was the equipment identical and from the same vendor? Was the equipment stored in the same location and in the same fashion prior to the package bees installation?
Are the hives in an low-visibility area or visible by people passing by? ...since there wasn't anything for them to be foraging on I'm thinking of a possible intentional insecticide spraying by someone, but that person was driven away by the angry bees before they could spray the second hive.
Were the two hives fed the same feed from the same batches...sugar syrup, pollen patties? Was the syrup given in identical containers? ...feed prepared in same container? ...possible contaminated container or feed used on one hive but something different used on the other one.
To the experts...what disease is there that can run rampant through a population of honey bees (can't really call it a colony yet as it sounds like it never got established) and completely kill it in 10 days? To me, ten days just seems too short of a time period for something non-chemical to wipe out that many bees, provided there was that many dead bees in/around the hive and not simply missing. Of course, if there is a disease that could take a new package out that fast I'm all ears to hear about it...my education continues.

Ed