CNN Films' first commissioned documentary, The Flag, explores the mysterious disappearance of an American flag featured in one of the most iconic photographs from the World Trade Center on September 11, 2001.

Directed by Michael Tucker and Petra Epperlein, the 90-minute documentary is based on a book by David FriendVanity Fair's editor of creative development and formerly LIFE magazine's director of photography.

Twelve years ago, an American flag raised on a boat docked near the Twin Towers survived the devastating attack. The flag - which was removed from the boat by an unknown person - was later raised by firefighters above the wreckage of the collapsed buildings on the evening of the attacks.

Thomas Franklin, a photographer with local New Jersey newspaper, The Record, captured three firefighters raising this flag in a photograph that was soon seen as archetypical of the disaster. Shortly after the photo was taken, the original flag disappeared, leaving many to question its whereabouts.

Watch the video below for a preview of how the filmmakers uncover the flag's mysterious journey. (Can't see the video? Click here to watch it on cnn.com).

The Flag airs on CNN Wednesday, September 4, at 9 p.m. ET.