Might as well share my story; perhaps did years ago here it is again, briefly:
Got off the Metro-North train at Grand Central from Poughkeepsie for my daily grind at 45 Rockefeller Plaza, about 5 miles north of the battery and Ground Zero. Walking to work about a mile away, nothing unusual. Arrive at the office and one of the partners of the firm wave me over to the television and says that a plane hit one of the towers. As we were watching the news report, the second plane hit...and we saw it live on the tv screen. It was astonishing.
As we were talking about the first plane hit, we thought it was possibly an error. But after the second hit, we realized it was a planned attack.
After a bit, I looked outside the window and looking south, saw all the black smoke.
After about I think a couple of hours, they closed the building completely and evacuated everyone, and this wasn't the only building that was shut down that day. And unbeknowst to me at the moment, the city also shut down Metro North for a few hours.
So, everybody outside had nowhere to go and literally were open to aerial attack.