Visitors walk along the wall of names of passengers who perished in the 9/11 terrorist attacks on the eve of the 13th anniversary of the attacks at the Flight 93 National Memorial Visitor Center Complex in Shanksville, Pennsylvania, on September 10, 2014. #

The sun rises prior to the ceremony marking the 10th anniversary of the crash of United Flight 93 at the Flight 93 National Memorial on September 11, 2011 in Shanksville, Pennsylvania. #

Candles in memory of the 40 passengers and crew of Flight 93, are carried to the Wall of Names at the Flight 93 National Memorial on Wednesday, September 10, 2014. Thursday marks the 13th anniversary of the September 11 terror attacks. #

Yachiyo Kuge, the mother of Toshiya Kuge who was a passenger on Flight 93, places origami birds near his name, at the Wall of Names at the Flight 93 National Memorial on September 10, 2014. #

Visitors walk along the wall of names of passengers who perished in the 9/11 terrorist attacks on the eve of the 13th anniversary of the attacks at the Flight 93 National Memorial Visitor Center Complex on September 10, 2014. #

Navy Quartermaster Matthew Konchan of Johnstown, Pennsylvania, stands in a field of black-eyed Susan as he waits to participate in a wreath-laying ceremony with Secretary of the Interior Sally Jewell during a memorial service at the Flight 93 National Memorial on September 11, 2013 in Shanksville. #

The Wall of Names containing the names of the 40 crew and passengers on Flight 93 at the Flight 93 National Memorial on September 11, 2013. The wall follows the plane's flight path to a boulder, rear, that marks the impact site. #

Kevin E. Newlin, left, and Jeff Reinbold of the National Park Service lead a media tour of the Flight 93 Visitors Center Complex construction site on September 10, 2014. #