And to me, that seems like a stupid mistake for the conspirators to make. If Cordite is being used for naval guns, odds would be good that the Pentagon would have people that could recognize the 'unmistakeable' smell and give away that fact that there was a cordite explosive used. At least better odds than someone on the police and fire crews would.

I agree, it is a stupid mistake. But it shouldn't be dismissed on the unfounded assumption that conspirators would have been "too smart" to make such an error. In fact, it seems to me that an anomaly such as this should warrant further investigation.