This film contains very disturbing images,” warned Jon Snow at the beginning of Sri Lanka’s Killing Fields. It would, he continued, depict “death, injury, execution and evidence of sexual abuse and murder”. He was right too, though when the final credits rolled you couldn’t help but feel that the worst lay somewhere off screen, less in the atrocities shown than in the moral debasement that had led to them being filmed in the first place, and the terrible banality of the conversations that went on as they were filmed. Two utterly distinct kinds of footage had gone into the making of Channel 4’s account of the closing weeks of the war against the Tamil Tigers. Firstly, there was video filmed by refugees trapped in the appalling “no fire zones” established by the Sri Lankan government, footage knowingly recorded to document a crime. And then there was video recorded by the criminals, as a souvenir of their own barbarity. And grim as the former was, it was the latter that truly shocked and that provided incontrovertible evidence that war crimes had taken place.