One dark night in Rwanda, a man who called himself Jean-Pierre warned the UN about a plan to exterminate Tutsis at a rate faster than the Nazis killed Jews.
The stalemate over sending peacekeepers shamed the West
In a lamp lit room in Kigali, Jean-Pierre offered to lead the UN to arms caches in return for asylum for his family, but UN officials in New York refused permission. Nobody knows "Jean-Pierre's" fate, but we do know the fate of those he tried to help.
Because three months later - in the spring of 1994 - gangs of renegade soldiers and machete-wielding street kids organized by the extremists of Hutu power set about murdering their Tutsi countrymen and leading moderate Hutus.
They killed at least 800,000 in 100 days, aided by ordinary men and women who were somehow convinced this was their "umuganda", their work and civic duty.
This was not tribal frenzy, not anarchy, but the work of an organised, hierarchical and obedient society. One that would certainly have noticed if the rest of the world had said "Stop It" and backed the warning up with a little force.
But while the UN voiced its disapproval, it declined for many of those 100 days even to use the term "genocide".
Over half a century after the world swore "Never Again" to the Holocaust, what are we to make of this exercise in what political scientist Norman Geras has called balefully the "Contract of Mutual Indifference"?
It wasn't that the rich, developed nations - not to mention landlocked Rwanda's African neighbours failed to intervene in Rwanda. Given the debacle earlier that year of Somalia, when 18 US army rangers died in a humanitarian mission to Somalia, a refusal to intervene might at least have been understandable.
The sin, if you want to call it that, was that the world was already there.
A force of UN peacekeepers had been despatched to Rwanda in 1993 to help enforce an emerging peace deal between the Hutu government and invading guerrillas of the Tutsi-led RPF.
Piles of bones show the scale of the slaughter
They'd been kept short of weapons, ammunition, vehicles, medicine, you name it. (It has to be said this was partly the fault of some of the governments who sent them there, like Bangladesh). The helicopters didn't even have hostile environment insurance, and were flown out when the killing started.
Then the UN voted to withdraw all but a handful of the peacekeepers (only to try to put them back when most of the killing was done). It has been claimed that even with the support of Western troops, flown in to evacuate Europeans, there weren't enough to stop the murders.
But whatever aggressive action they might have taken, some of the UN troops were actually guarding civilians.
When Belgian troops were pulled out of the Don Bosco camp - codeword Beverly Hills - the killers who had been driving around the camp with their machetes, AKs and fluorescent wigs moved in and killed about 2,000 men women and children.
Shortly afterwards - with UN troops still protecting many civilians - the British team at the UN was privately claiming it would be a "tragic fiction" to suppose the UN could help protect any more beleaguered Tutsis.
The ultimate insults to the dying are now well known. The US State Department's spokeswoman Christine Shelley - acting on orders - declined to use the term "genocide" unqualified, insisting on saying only "acts of genocide" were occurring.
The department's legal team feared that recognising the G Word would oblige the US to intervene because of the UN Genocide Convention. In fact the convention mandates no such thing, merely makes it a possibility. The lawyers knew this but politicians feared the public wouldn't follow such subtle reasoning.
Then, when the UN did decide to summon up an intervention force, the US delayed over the despatch of armoured vehicles. The arguments ranged from what colour to paint the vehicles to who would be paying for the painting.
And when they did arrive - they didn't have radios. Although the killing was already over.
And then there was the suggestion of jamming the Hate Radio station that was giving the killers orders. The trouble with that - apart from a few technical hassles that could surely have been overcome - it would surely breach the US's constitutional commitment to free speech.
There were other episodes of mass murder in the 20th Century. But - other than the Allied planes flying over the Nazi death camps - there has been no other such demonstration of the Contract of Mutual Indifference in a country where the onlooking world - in an age of mass media - has had a military presence.
Hence the title of Panorama's 1999 film "When Good Men Do Nothing" a phrase attributed to the English philosopher Edmund Burke, and his condition for what he called The Triumph of Evil.
We could also, I suppose, have called it And Who Is My Neighbour? That, you may recall, is the sardonic question a lawyer asks in Saint Luke, a question that prompts the Parable of the Good Samaritan.
One official who originally backed the do nothing policy, Anthony Barnett, told Panorama he could never have believed he would be a bystander to genocide.
"You should be ashamed," he told himself on camera. I think he would like to feel he speaks for the rest of us.
Steve Bradshaw made his first Panorama programme on Rwanda - A Culture of Murder - in the weeks after the genocide. He has made two other films on Rwanda including the award winning When Good Men Do Nothing, which investigated the failure of the international community in Rwanda in detail.