Look back at some of the work that went into building the memorial to United Flight 93 in Pennsylvania.
Tokens honoring Flight 93 sit near the fence surrounding the permanent memorial's construction site in May 2011.
Jim Rogash/Getty Images
Jim Rogash/ Getty
U.S. Air Force
Frederick M. Brown/Getty Images
New York Magazine/Twitter via CNN
Bryn Lennon/Getty Images
Beverly Hills Police Department
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