How extensive was Western complicity in Soviet crimes?

Diana West has again raised the question of Western complicity in Soviet crimes in "American Betrayal: Nuremberg and the Nazi-Soviet Pact."  This is the 75th anniversary of the Nazi-Soviet Pact.  This particular case involves the suppression by the American and British authorities of evidence contained in the secret protocol of the Hitler-Stalin Pact.  It was a widely known historical fact that the Soviets had come to an agreement with the Hitler regime to divide Poland between them.  The German invasion of Poland was the immediate cause of the Second World War.  It was followed two weeks later by the Russian invasion of their agreed upon eastern part of Poland.

It was necessary to suppress this evidence because the German high command  was being charged with “conspiracy to wage aggressive war.”  It would damage the image of the Nuremberg trail as a "model of international justice" if it was pointed out that the Soviets, sitting in judgment of the Germans, were themselves guilty of the same crime.  The Soviets originally planned to charge the Germans with committing the Katyn Forest Massacre.  This was the execution in Katyn Forest and other locations of 25,700 Polish prisoners captured by the Soviet.  Their case was so weak that they thought it wise to not include it.  The whole proceeding was described by Judge Learned Hand  as "A step backward in international law."

The Western officials had good reason to protect their Soviet "allies."  They were trying to maintain the good will of their Russian counterparts.  They also did not want other matter to come to light.  Diana West mentions the forced repatriation of over two million eastern Europeans to the Soviet Union.  But there is much more they wanted to conceal.  The Western role in the slave trade and the engineered famine are the two most indefensible policies.  Germany was transformed into a paradise for looters.  Even the chief U.S. Prosecutor and Supreme Court Justice Robert Jackson took part in this orgy of looting, obtaining two grand pianos at bargain basement prices.    

She points out that the perpetrators of these crimes were "allowed to slip away unrecognized, unjudged, unpunished."  Why would these criminals, whose death toll exceeded the Nazis, be allowed to escape judgment after the fall of the Soviet Union?  Diana West provides a partial answer.  The decisive opposition to a Nuremberg style trial came from the West.  What did the leaders of the West have to hide?