I found something really interesting here on Wikipedia: "In 1945, Hitchcock served as "treatment advisor" (in effect, a film-editor) for a Holocaust documentary produced by the British Army. The film, which recorded the liberation of Concentration Camps, remained unreleased until 1985, when it was completed by PBS Frontline and distributed under the title Memory of the Camps."

The movie can be seen on Google Video or over at PBS Frontline: "As the troops entered the German concentration camps, they made a systematic film record of what they saw. Work began in the summer of 1945 on the documentary, but the film was left unfinished. FRONTLINE found it stored in a vault of London's Imperial War Museum. (...) As the film's history shows, it was a project that was supervised by the British Ministry of Information and the American Office of War Information. And during that summer of 1945 some of the documentary editing was done under the direction of Alfred Hitchcock. (...) Some of the horrors documented took place literally moments before the Allied troops arrived, as the Germans hurried to cover the evidence of what they had done.

Twenty years after FRONTLINE first aired it, "Memory of the Camps" remains one of the most definitive and unforgettable records of the 20th century's darkest hour."

Teachers: Using "Memory of the Camps"