There was an alleged explosion in Foggy Bottom. Actually IIRC, media references were to the State Dept. (not the more general area of Foggy Bottom), and State was evacuated. But the truth is that every federal building in DC and No. VA was evac'd by 10:30AM. It was also reported by CNN as a "car bomb" at State the morning of 9/11. I clearly remember that.
But none of this turned out to be true.
Even on that day, 9/11, it seemed to me as if someone had reported the threat of a "car bomb" at State, and it was garbled by the media in realtime reporting to mean an actual car bomb.
Also, I drove around downtown DC the evening of 9/11. There was no evidence of any "car bomb" or any other kind of damage anywhere, aside from the Pentagon. There was certainly no assertion of any bomb in the media the next day, and it would be extremely difficult to overlook such a thing if it really happened.
I'm also trying to cleanup this issue about the "explosion" which occurred some time after the plane hit the Pentagon, because there's a lot of confusion about it.
Yes, there was an explosion, no doubt about that. I heard it about 20 minutes after the plane struck. I know this time is accurate because I had left the house just before 10AM to get to a biz appointment, and heard the explosion 5 to 8 minutes later while stopping to buy aspirin at a CVS down the street.
This explosion was from an LP gas tank at the Pentagon, as relayed to me by an EMT/fireman with 15 years experience. I know the guy well and have no reason to disbelieve him. But you could hear and feel it from 3 miles away (it shook the windows at the CVS pharmacy), which would certainly explain why folks in Foggy Bottom and elsewhere in DC would have heard this same explosion.