Hat tip to Stratfor giving a hint to the role of the public in the case of Naser Jason Abdo:
planning to attack a restaurant frequented by soldiers from Fort Hood (in July 2011)
The public's role:
On July 27, 2011, Abdo raised the suspicion of the staff of "Guns Galore" in Killeen Texas by buying an unusually large amount of smokeless gunpowder, three boxes of shotgun ammunition and a magazine for a pistol. A clerk notified the Killeen Police Department who, in turn, tracked Abdo to the America's Best Value Inn and Suites via the taxi that he had taken to make his purchase. Guns Galore was the store in which Nidal Malik Hasan bought a pistol used in the Fort Hood shootings.
Link:http://en.wikipedia.org/wiki/Naser_Jason_Abdo

I expect the Guns Galore staff and management were all too aware of the purchases being suspicious, even allowing for a two year gap. Would another local gun store have done the same thing?