The acclaimed director Sam Mendes has made his first documentary. What They Found follows Sergeants Mike Lewis and Bill Lawrie, two cameramen with the British Army who were part of a military unit that moved through Germany in 1945. Their cameras captured a trip to a “typhus hospital” that turned out to be the notorious Nazi concentration camp Bergen-Belsen. No one had ever seen anything like it. In the 1950s, those recordings were given to the Imperial War Museum by the British War Office, and the museum later conducted a chain of interviews that included firsthand accounts from Lewis and Lawrie. Using only the footage and audio from the two videographers, Mendes delivers a devastating film, its release timed to the 80th anniversary of the liberation of Bergen-Belsen—April 15, 1945. —Henry McGrath