For many years, I have been looking for the missing picture: a photograph taken between 1975 and 1979 by the Khmer Rouge when they ruled over Cambodia...On its own, of course, an image cannot prove mass murder, but it gives us cause for thought, prompts us to meditate, to record History. I searched for it vainly in the archives, in old papers, in the country villages of Cambodia. Today I know: this image must be missing.