After almost 25 years now, there are more things we still can learn about that day. Silverstein had signed a 99-year lease for the World Trade Center complex just weeks before the attacks. Silverstein has stated that he typically attended meetings at the World Trade Center every morning. However, on 9/11, he did not go to the office due to a medical appointment. This detail has frequently resurfaced in documentaries, news reports, and online discussions as people revisit the events of that tragic day.
They were already there they started capturing and killing known enemies immediately it ramped up as military logistics ramped up. John Kiriakou has spoken a fair bit about the days weeks and months after 9/11 on the podcast circuit.
https://www.youtube.com/watch?v=WSFo5cNze2U