premise: Evidence indicates that this conversation was the only notice received by either FAA headquarters or the Herndon Command Center prior to the second crash that there had been a second hijacking.
hypothesis: The phone conversation was the only notice received by FAA headquarters or Herndon Command Center prior to the second crash to even notify authorities there had been a second hijacking of a plane and this led to a delayed emergency military response and the other flight being directed into the second tower. 