being built but our ability to have that library coverage enabled us to go back and to rebuild essentially over time. >> building a scale model accurate to the centimeter. >> the tracking down and taking down of osama bin laden was kind of a classic example of successful u.s. of intelligence. >> james clapper coordinates the efforts of all american intelligence agencies. >> that was a huge moment for me and a lot of us in the intelligence community, particularly those of us who lived through 9/11. it was closure. it really was. >> since 9/11, threats to the u.s. have grown more sophisticated. and so have the tools to combat them. today, the cardboard model of bin laden's compound has evolved