For over 25 years, the Twin Towers defined the New York skyline and epitomized everything the United States stood for. And then in just a couple of hours, they were gone. 9/11 remains the deadliest act of terrorism on American soil, but how did an attack of this scale happen and why were we so unprepared for it? Through investigative reports, declassified documents, and interviews with first responders and those who were involved at the highest level, we reveal ten fatal mistakes that together led to that horrific, tragic day.