"I wrote to the FBI. I never heard from them, but I am hoping they put "meeting on mass transit" in their database."
I hope they did too, but my confidence is low. Don't you wonder whether they would have listened to you, if you had heard something about the WTC plot on that train ride, and reported it to them? My cynical side says that they would have written you off as crazy, and really regretted it later.
Yes, they probably would have. But then, I myself probably wouldn't have believed what I had heard, either. It's hard to remember what life was like before 9/11.