The art of using film footage to terrify an audience was practically invented by Alfred Hitchcock. His mastery and ability to meticulously frame every shot so his audience would be spellbound has been emulated by generations of directors after him.But when director Sidney Bernstein approached Hitchcock to be the supervising director of German Concentration Camps Factual Survey, a documentary commissioned by the British government to document the liberation of the concentration camps, Hitchcock did not need to resort to cinematic trickery or artifice to capture the sheer horror found there.Night Will Fall, then, is a documentary about a documentary. The film, which aired on HBO Monday night, chronicles the efforts of British, American and Russian filmmakers to document the tragedy of the concentration camps with the purpose of showing their finished product to German audiences. The explicit purpose was simple: bring each and every complicit German out of post-war denial and show them that, yes, this really happened and they are responsible.But as the war came to a close, and the Cold War loomed, Germans were seen as a potential ally for the West and work on the documentary was shelved, the footage never to be seen by the general public again.Until now.In 2010, the Imperial War Museum worked on restoring this long-lost footage. The HBO documentary, which splices together clips from the original along with new testimony from the veteran cameramen and the survivors of Dachu, Bergen-Belsen and Auschwitz, is a moving testament to the power of the moving image.The documentary is at its most powerful when it shows the men and women who were there recalling their traumatic experience today.“I peered into hell. It’s not something you quickly forget. It’s still hard for me to describe,” Sgt. Benjamin Ferencz of the US Third Army, says in one clip.But the witnesses and survivors don’t need words to express what they saw. On Ferencz, the sadness and fear is clearly etched on his face. The distant look in his eyes makes it clear that what he saw was humanity at its worst.Although hard to believe given the subject matter, there is an uplifting element to Night Will Fall. Amid the tragedy, the footage depicts the survivors greeting their liberators. It shows, clearly, in raw, black and white, the look of relief on their faces. It shows them being clothed and fed and – slowly – as the film describes, becoming “human again.”For a split second, the film shows the look of happiness on a young boy’s face as he adorns a sweater vest, probably the first real piece of warm clothing he has worn in years. There, one can see the even in the worst darkness and despair there is hope.The documentary also exposes the political nature of the genre. It is interesting that a government that was so invested in bringing this footage to the masses immediately shelved it when its original purpose no longer suited their interests.“One day you will realize that it’s been worthwhile,” Bernstein wrote to one of its editors, Peter Tanner.And while that day may have come 70 years after their collaboration began, it is gratifying to see that his words came true.