What you need for large-scale genocide is not an inexplicable eruption of evil - you need bureaucratic determination married to routine malice

"No scruples, only stubbornness," said a German veteran in The Nazis (BBC2). He was describing Operation Barbarossa, Hitler's invasion of Russia, but the translation of his word "sturheit" struck a slightly odd note - as if the shooting of civilians was the result of a whimsical refusal to change one's mind. "Obdurateness" might have been better, or something like "unswerving dedication". But however you express this rather Teutonic concept in English it was clear that it was at the heart of what was to follow. There were singular horrors in this account of the road to Treblinka, but this film confirmed that it does not take singular people to commit them. What you need for a large-scale genocide is not an inexplicable eruption of evil - you need bureaucratic determination married to the kind of routine malice that is always ready for recruitment.

This film, like others in the series, was remarkable principally for its interviews and its scholarly footnotes. It has found striking images in the archives, of course; last night for instance the account of an early massacre of Jews in Lithuania was illustrated with photographs of the event - as men were bludgeoned to death with a crowbar a large crowd looked on, including a woman in a smart floral dress smiling broadly. But it was the photographer's account of how one of the killers had stood on the bodies to play the Lithuanian national anthem that really brought home this ghastly festival. Occasionally the archive pictures strike up discordant echoes, echoes intended by the film-makers I think, but handled with considerable tact. Looking at footage of Berliners in 1941, sunbathing by the city lakes, you couldn't help but think of the half-dressed women you had already seen, trembling in a Lithuanian wood as they waited for a bullet in the back of the head.

The Nazis didn't offer a conclusive answer to the question of how much those sunbathers knew - but they made it very clear that the people who worked the machinery of the Holocaust were not moral aliens - monsters discontinuous with our own small failures of imagination or courage. There were scruples - however inadequate they seem to the the scale of the crime. Soldiers became distressed by their duty and the difficulty of maintaining their morale was one of the motives for developing less hand-crafted methods of extermination. What's more, even the architects of mass murder knew that this was a project that could never hold its head up in public; a wartime telephone operator told of a striking conversation between Himmler and Bormann, in which the former accidentally used the word "liquidation" rather than the approved euphemism, "evacuation". Bormann lost his temper and threatened to report the breach of protocol to Hitler.

What all this suggested was that the mystery of the death camps was not the disappearance of common conscience but its daily defeat. And in that respect "sturheit" was an indispensable ally - making a virtue out of vice. To shoot children became "brave", to falter in murder an act of cowardice. An old lady was asked how she could reconcile the "sweet, chivalrous" Heydrich she knew with the man who ordered the murder of thousands of civilians. "It's actually quite logical, you see," she answered calmly. "If someone is conscientious like Heydrich and does everything thoroughly as he always wanted to, then he can't help it." By this light, the meticulous bookkeeping of the Einsatzgruppen was not a symptom of moral blindness but a blinkering device in itself - something so formally correct could surely not be a record of bestiality. Watching Heydrich and Himmler on the terrace at the Berghof you saw two ambitious managers in business suits, burying all human concerns beneath a larger goal. Are such men still out there? You bet they are, which is why The Nazis is the most significant programme currently on air.