Now, over five decades after the war's end, governments are launching a concerted drive to return looted art. At the end of this month, representatives of dozens of countries will meet in Washington DC, at the Conference on Holocaust Era assets. Plundered art will be high on the agenda, as delegates try and piece together the parts of the jigsaw, scattered all over the world, that makes up the art collections stolen and broken up.
There is much to discuss. A report released yesterday by the London-based Holocaust Educational Trust reveals how post-war Britain stonewalled attempts by wartime survivors to reclaim their artworks, and British officials even helped a convicted war criminal reclaim assets confiscated by Allied troops. The post-war government failed to impose safeguards of looted works of art passing through Britain, and cut-off restitution claims after 30 June 1949. Holocaust survivors, or their heirs, who attempted to reclaim their artworks were refused, even though well-connected German aristocrats and British establishment figures such as Lord Rothermere all received their collections back.
The Washington Conference is the latest stage in an unprecedented world- wide bout of soul searching over the fate of the property of the Jews killed in the Holocaust, and of other victims of Nazism that began with the Swiss banks and the long-running battle to recover monies deposited in now dormant bank accounts. The wartime allies that pressured the Swiss to open their books and admit the full extent of their economic collaboration with the Third Reich suddenly realised that their own hands were less than clean.
The international restitution campaign follows a conference earlier this year when 39 nations, led by the United States and including Britain, France and Germany, pledged to identify works of art looted by the Nazis, and return them. Now national museums, including British institutions, are setting up databases to determine the provenance of the works in their collections. Galleries could be forced to dismantle collections that have hung on their walls for decades, even if they believed they legitimately owned them.
Why is this happening now? A world-wide desire to finally close the last chapter of the Holocaust and the collapse of the Communist bloc have both spurred on the restitution drive. The raising of the former Iron Curtain allowed Holocaust survivors to finally claim their rightful assets, no longer fearing that their governments would confiscate anything that was returned.
Psychological factors also play a role, says Stephen Ward of the Holocaust Education Trust. "There is a sense that the wartime generation, both victims and those involved in looting, want to settle unfinished business while they are still alive."
Britain, too, has some unfinished wartime business. Enthusiasm for battling the Nazis did not make the peacetime transition to returning artworks stolen by the Germans to their rightful owners or heirs. Officials in the British-run zones of post-war Germany and Austria based their policies of restitution on the First World War principles of dealing with governments rather than individuals.
Meanwhile, Lord Rothermere managed to recover first his collection of masterpieces from Hungary, and then, in 1947, a further 15 works in Munich. Even a conviction as a war criminal was not necessarily a barrier to compensation from Britain. In 1952, the arms manufacturer Alfred Krupp claimed compensation from Britain over art treasures taken from his villa in 1945. By the early 1950s and the onset of the Cold War, Krupp, like many pre-war German industrialists and financiers of the Nazi party, had been judged by the west as more useful in helping rebuild West Germany, than serving out his time in prison.
British officials, fearing "political embarrassment", according to the HET report, even tried to recover some of the Krupp property for the man whose weapons had killed so many Allied troops. "The case histories preserved at the Public Record Office suggest the rules could be bent for the powerful and influential, even, apparently, the families of some former Nazis," the HET report details.
This appears to have included relatives of Heinrich Himmler, who, it seems, were allowed to retain some looted art. As he had died, his name was not on the list of war criminals whose property was automatically forfeited.
British art dealers and auction houses failed to take special care to check the provenance of art they handled after the war, the HET report adds. "For the trade, the only important question about a work remained its authenticity - was it genuine?"
Sculptures, drawings, oils, water-colours, tens of thousands of works of art disappeared into the Third Reich's warehouses, and the homes of its leaders such as Hermann Goering. Whole museums, especially in the Soviet Union, were dismantled, boxed up and carried off. Private owners, especially Jews and Slavs, were sent to concentration camps, and their collections sent on to Berlin for the delectation of the Nazi leaders.
Paintings by artists like Cezanne and Van Gogh could be had for the picking as the Third Reich thundered its way across wartime Europe. France's museums offered the best bounty for the Nazis. Alfred Rosenberg, the supposed "Philosopher King" of the Third Reich, later hanged as a war criminal at Nuremberg, set up a special unit in order to plunder the country's chateaux and museums: the "Eizenstab Rosenberg".
In November 1940, Hermann Goering, one of the most rapacious members of the Nazi leadership, who fancied himself as an art connoisseur, issued a secret order detailing how objects plundered from the Louvre would be disposed of. They would be divided into three categories: for the Fuhrer himself; for Goering's own collection and others, to be sent to German museums.
Goering would travel across the Reich himself after his spotters located suitable pieces. Hitler would receive visits from dealers in plunder such as Maria Almas-Dietrich. That she had given birth to an illegitimate daughter fathered by a Jew, and later married a Jewish Turk, did not seem to impede her trade with the Fuhrer, and she sold him 270 paintings.
Many of these last POWs have found new homes in some of the world's most prestigious art museums. The Louvre, for example, has about 2,000 works of art recovered from the Nazis at the end of the war, that have not been returned to their owners or their rightful heirs. Those 2,000 pictures have been posted on the Internet, at a site run by the French Ministry of Culture (http://www.culture.frwww.culture.fr) for potential claimants to peruse - and several ownership claims have been received.
About 100,000 works of art were looted from France by the Nazis, of which 60,000 were returned. Over 45,000 were returned to their owners, many of which were museums. But after 90,000 French Jews were killed in the Holocaust, many of them whole families, some could never be given back, even if the desire to return them had existed.
Which it often did not, according to declassified US Intelligence documents. Many art dealers made a tidy living out of buying up French Jews' collections on the cheap and selling them on to the Nazis.
The report of the US Art Looting Investigation Unit's final mission to Europe, in the summer of 1946, details French reluctance to pursue economic collaborators with the Nazis: `"Despite the extensive documentation in French hands, some of it presented to them by this unit, the French have made disappointingly slow progress in the prosecution of their own collaborationist dealers, and there were many indicators this summer that most of the collaborationist dealers were continuing business as usual."
The US was a fruitful market for looted art, the report adds: "Many of these dealers had already re-established their contacts with dealers in the United States, and some of the objects acquired by looting and forced sale may have already been transferred to this country."
The Nuremberg trials classified Nazi looting of art as a war-crime, and from 1944 Britain and the US agreed that they would find and seize all Nazi assets. But seizure of looted Nazi assets did not automatically mean they would be used for restitution for Nazi victims. During 1945 and 1946, items taken by the British from properties formerly owned by Heinrich Himmler were used to decorate British military offices in the British- occupied zone of Germany.
Now, decades later, the world's conscience has finally awoken. Some artworks will never be found, for many masterpieces languish in the cellars of Russian museums, while others are out of reach in the vaults of Swiss banks, or were listed in files in government archives that have long since been destroyed.
But this month in Washington DC, governments are being driven by morality, however belated, instead of expediency.
Those paintings that survived Alois Miedl's 1944 convoy across the Spanish border might yet find their way home.
Adam LeBor's book, Hitler's Secret Bankers: How Switzerland Profited from Nazi Genocide is published by Simon and Schuster.