Poland's been traumatised by the loss of its ruling elite in a plane crash. Ironically, they were on their way to commemorate the massacre by Russians of 22,000 Polish officers. Only now is the full truth emerging of what took place - and why Britain turned a blind eye.
Executions normally take place hurriedly, but in this case the killers were in no rush.
The victims were taken from their prison camp and put on a train for two days without food and water.
When they arrived at their final destination, they were bundled onto coaches with windows smeared with cement to obscure their view. After a short drive, the men were directed one by one to the rear door of the vehicle.
As each man stepped into the gloomy light of the Russian forest, he would have had no doubt as to his fate.
Brutal: A scene from Katyn, a Polish film about the notorious massacre
Ahead lay an L-shaped pit with the fresh corpses of his fellow Polish officers. But before the full horror could have set in, he would have been grabbed by the arms of two strong Russian soldiers wearing the uniform of the Soviet secret
If he struggled, his hands would have been tied and a choke knot applied to his neck. Others had greatcoats tied over their heads; some had their mouths stuffed with sawdust. Those who still tried to break free had their skulls smashed, or were repeatedly bayonetted. There could be no escape.
Many were simply led to the edge of what would imminently be their grave. Held on either side, the victims were approached from behind by an NKVD man equipped with a German Walther 7.65mm pistol.
The relatively small recoil, compared to that of heavier Russian pistols, made the task far easier on the executioner's wrist, an essential requisite for a killer with so many men to despatch.
The shot was fired at the base of the man's skull, and if the job was done correctly, the bullet would have exited through the forehead. Death was instantaneous, as one by one the Polish officers filled the mass grave.
The location was a forest outside the small village of Katyn just west of the city of Smolensk. And it was here - and at two other sites between April and May 1940 - that Stalin's killers shot some 22,000 Polish officers, who together constituted the cream of Poland's military elite.
The full horror of what took place at these three locations has gone down in history as the 'Katyn massacres'. And since last Saturday, that name has taken a shocking new resonance.
Because it was to Katyn itself that the Polish president, Lech Kaczynski, and 95 other civilian and military leaders were travelling to mark the 70th anniversary of the massacres last weekend, when their plane crashed in thick fog, killing all on board.
A thorough investigation into the cause for the crash has already begun, and a swift report promised. What a contrast to the aftermath of the massacres themselves, which saw many decades pass before the truth began to emerge.
For years, the blame for the killings was alternately attributed to the Germans and the Russians, both of whom were all-too capable of brutality on such a scale. Added to this were stories of cover-ups by the British and American political establishments, and there have been the inevitable slew of conspiracy theories.
But today we can be broadly certain of what happened, thanks largely to the excellent historical investigations of the Polish Institute of National Remembrance, headed by Janusz Kurtyka, sadly one of the victims of the air crash. In addition, a new book called Katyn 1940 by Polish author Eugenia Maresch also collects together much documentary evidence about how the Western powers reacted to the murders.
As a result we can at last form a near- complete picture of what took place at Katyn - and in its bitter aftermath.
It is often forgotten that when Hitler invaded Poland on September 1, 1939, Stalin followed suit just over a fortnight later. Faced with the combined might of a twin attack, it was impossible for the Poles to hold out, and by the end of the month the country was carved up by two of the world's most brutal regimes.
As the Germans started enacting their infamous horrors against the Polish population, the Russians were embarking on a similar campaign of brutal suppression.
In October, Lavrenti Beria, the head of the Soviet secret police, issued an order that officers should be separated from among the hundreds of thousands of Polish PoWs.
One of the officers was Zdzislaw Peszkowski, a 21-year-old who had just graduated from the military academy. A few years ago, shortly before he died, I interviewed Peszkowski and he was able to recall the events of 1940 with astonishing and deeply moving clarity.
'We were packed into cattle trucks and sent off,' he said. 'In mine there were about 70 of us, and we were in that truck for one month. One of my friends with me had been a Russian prisoner before, and he told me that if the Russians gave us herrings, I should not eat them, because if you do not drink water with them, you are in trouble because of their saltiness.
'However, some of my comrades did eat herring, and it was a disaster. The men's lips were so dry that they bled as if they had been cut with knives.'
The officers did receive water at the occasional stop, during which they were able to gasp in some fresh air and dispose of the bodies of those who had died.
Eventually, in early November, the convoy arrived at a large church in Kozielsk in north-eastern Poland, where Peszkowski and some 4,000 other officers were quartered in a PoW camp.
The prisoners sat there for months, afraid of what was going to happen, but few guessing their true fate. As Peszkowski said: 'We did not think it possible that the Russians would kill us without mercy.'
In Moscow in March 1940, the men's fate was finalised. That month, Beria sent a memorandum to Stalin, proposing that the officers should be shot in order to crush any potential insurrection.
The Soviet leader agreed, and scribbled his expansive signature over the top of the paper. His approval was endorsed by three members of the Politburo, all of whom added their names under that of their leader.
The Russian eagerness to slaughter Poland's military leadership was not simply born out of savagery. Many believe that Stalin reckoned that such ruthless tactics would permanently weaken the Poles, and make them a much easier people to subdue.
With the acceptance of the Beria memorandum, events moved swiftly, and at Kozielsk as well as other camps, the officers were despatched eastwards on trains.
'They started to send groups away every few days,' Zdzislaw Peszkowski recalled. 'For a while, these departures were celebrated, as we were given the idea that they were being sent off to a new kind of life in a very good place.'
This optimism was increased by the fact that the Russians would cynically inoculate the prisoners against diseases such as cholera and typhus. However, when the empty trains returned after a few days, the prisoners started to wonder where their comrades had really gone.
Peszkowski remembered how a woman who worked in a local hospital started crying when she spoke to one of the prisoners. 'He asked her what the problem was, and she said: "They are lying.'''
The next day, the woman disappeared.
Accounts of exactly what did take place at the execution sites are understandably scarce. Few of the Russian soldiers who took part ever spoke of what they had done.
But Janusz Laskowski, a Pole now living in London, recalls how, as an 11-year-old-boy, one of the Russian executioners had been billeted at his mother's house.
Every evening, Janusz had listened as the Soviet soldier taunted him by describing his day's work. We now know that after being transported into the forest in trucks, the Polish PoWs were discharged into a barbed wire cage, which acted as a temporary holding pen.
From here, they were taken in groups to the edge of the killing pits, their hands bound.
Those who struggled were blindfolded or had coats thrown over the heads. But those who went quietly would have witnessed a monstrous sight.
In the broad, deep pit lay the bodies of their dead comrades. Those around the edges had been packed tightly, head to toe, like sardines in a tin, while those thrown into the middle were tossed in a disorderly pile.
Russian soldiers were trampling up and down on the corpses, dragging their latest victims into position like butchers in an abattoir. The new arrivals soon joined the dead, a single bullet shot at point plank range through the back of their skulls.
A diary later found on the body of Major Adam Solski, shot at Katyn on April 8, records the creeping horror of the victims as they realised the fate that awaited them.
'A transfer in the boxes of a black maria (it's frightening),' reads the final entry. 'We were brought somewhere into a forest like an outoftown resort. We were searched thoroughly. They [the Russian guards] were interested in my wedding ring and took away the roubles that I had, and also my belt, my penknife and my watch, which showed the time to be 6.30 . . .'
They were the final words he would write.
Only when the last of the Polish victims has been despatched did the executioners turn their hand to a more mundane task: shovelling soil over the bodies, smoothing over the ground and then planting conifer saplings over the site to hide their gruesome handiwork.
It was a clinical operation, but awesome in the scale of its savagery. Soon there were just 250 men left at Kosielsk and a further 182 at other camps. Some 22,000 had been massacred. 'I always think, why not me?' said Zdzislaw Peszkowski, one of the few survivors.
Away from Katyn, events were moving fast. After the German attack on the Soviet Union in June 1941, the Poles and Russians were forced to set aside hostilities to become, instead, the uneasiest of allies.
Desperate for all the support they could muster, the Russians released the remaining PoWs to join an army being hastily assembled under a Polish commander, General Anders.
'He came to us in prison to tell us we were free,' Peszkowski recalled. 'We asked him: "General, where are the others?" He said: "We are trying to find out."'
In fact, the world was not to find out what had taken place at Katyn until April 13, 1943, when the Germans announced their unearthing of the mass grave in the forest. For the Nazis, the discovery of a war crime that had been committed by the Russians was a propaganda coup - and they soon sought to exploit as much capital from it as possible.
Unsurprisingly, the revelations caused huge international tension. Two days after the German announcement of their find, General Sikorski, the prime minister of the Polish government-in-exile, discussed the murders with Winston Churchill.
According to a Polish record of the conversation, Churchill told Sikorski that he thought German claims that the Russians had committed the massacre were 'perhaps true'.
'We know what the Bolsheviks are capable of and how they know how to be cruel,' said Churchill.
But there was little he could do. His suspicions were outweighed by his determination to maintain the alliance with the Soviet Union and defeat Hitler. That policy was crystallised by the head of the British Military Mission in Moscow, who reported back to War Office in August 1941 that 'we've got to keep out of the affair as much as we can, and when we do intervene we must remember that Russia can help us to beat Hitler, and not Poland'.
Some have since taken this missive as proof of Britain's connivance in concealing the horrors of Katyn. But at the time, Polish leaders recognised that political and military pragmatism had to dictate the response of Britain and America.
Stanislaw Mikolajczyk, who would become the prime minister of the Polish government in exile after the death of General Sikorski in a plane crash in July 1943, admitted to Winston Churchill that a split in relations with the Soviets could be disastrous to the Allied fight against Nazism.
Besides, throughout the war, the evidence for Russian culpability for the massacres was strongly contested. Sir Bernard Spilsbury, the leading British pathologist and sometimes regarded as the father of modern forensics, wrote in April 1944 that it was 'not possible in my opinion to settle the controversy between the Russians and the Germans'.
The forensic evidence taken from bodies found in the Katyn graves led Spilsbury to conclude that they had been buried for a shorter period than was being claimed by the Germans, and that therefore the murders must have been carried out by the Nazis themselves.
Others were concerned about the reliability of documents that had been found on the bodies linking the Russians to the massacre, and some suggested that they may have been forgeries planted by the Germans to frame the Red Army.
This led Sir William Malkin, the senior adviser to the Foreign Office, to write: 'We are not likely ever to know the truth about this, but it should at any rate justify a suspension of judgment on our part.'
Even after Hitler's defeat, this policy was maintained by the British throughout the Cold War. For some British and most Poles, the whole episode stank of a shameful cover-up. But even until very recently, the evidence was still disputed.
Even some Germans suspected that the whole Katyn affair was little more than an invention of Goebbels, the German propaganda minister. As one former German soldier wrote to The Times in February 1971: 'We German soldiers. . . knew very well that the Polish officers were despatched by none others than our own.'
It was not until the 1990s that the truth finally emerged, when Russian leader Mikhail Gorbachev finally admitted that the NKVD was responsible. In 1992, his replacement, Boris Yeltsin, sent the Poles documentary proof, including the notorious Beria memorandum signed by Stalin.
As a result of the revelations, new exhumations were carried out at the killing sites. And one of those involved was Zdzislaw Peszkowski, the former officer who had so narrowly avoided death, and had become a Roman Catholic priest and the chaplain for the relatives of those massacred at Katyn.
'I wanted to make the exhumations sacred,' Peszkowski told me. 'We had Mass every day and prayers at 12 o'clock. The diggings were like opening the wound of our nation.'
Alas, with the death of 95 of their country's finest en route to honour the victims of the massacres, that nation now has cause for double sorrow amid the shadows of the Katyn forest.