Based on a proposal from Lavrentiy Beria, the massacre was approved by the Politburo of the Communist Party of the Soviet Union, including its leader, Joseph Stalin. Various Poles (such as military officers, police officers, and intellectuals) considered potentially problematic for the Communists were killed.
National Socialist Germany announced the discovery of mass graves in the Katyn Forest in 1943. The Germans brought in neutral journalists and a European Red Cross committee called the Katyn Commission, comprising 12 forensic experts and their staff, from Belgium, Bulgaria, Croatia, Denmark, Finland, France, Hungary, Italy, the Netherlands, Romania, Sweden, and Slovakia.
Wartime effects of Germany revealing the Katyn massacre
When the London-based Polish government-in-exile asked for an investigation by the International Committee of the Red Cross, Stalin immediately severed diplomatic relations with it. The USSR claimed that the victims had been murdered by the National Socialists in 1941. The Soviet Union and Communist Poland continued to deny responsibility for the massacres in the postwar period. In 1990, the Soviet Union officially acknowledged and condemned the perpetration of the killings by the NKVD, as well as the subsequent cover-up.
The revelation is argued to have caused a war between Polish and Soviet partisans. See National Socialist Germany and partisans/resistance movements: Internal conflicts among partisans and with the civilian populations.
The Allies are argued to have intensified the Holocaust propaganda in order to counter the effects of the Katyn revelation. See Allied psychological warfare: Anti-Katyn propaganda.
The Soviet Union has been argued to as another response to have created the Extraordinary State Commission which as one of its many allegations alleged that Katyn was a German massacre and started producing "evidence" supporting this.
Katyn at the Nuremberg trials
The Soviet Union submitted massive amounts of false evidence on Katyn including faked forensic evidence and false testimonies at the Nuremberg trials in an attempt to blame Germany. However, the other Allies refused to support (but did not explicitly reject) this particular falsification by quietly ignoring these charges in the verdict. The non-support may have been because Katyn was already being widely known to be a Soviet massacre, the massacre was not part of the Holocaust narrative, and the massacre was useful as propaganda against the Soviets).
Regarding more details, see the "External links" section.
The Extraordinary State Commission which produced this false evidence was also involved in numerous other atrocities as discussed in the article on this topic.
- WAR CRIMES TRIALS KATYN: How the Soviets Manufactured War Crime Documents for the Nuremberg Court
- Katyn: Unanswered Questions
- WAR CRIMES TRIALS KATYN: How the Soviets Manufactured War Crime Documents for the Nuremberg Court http://www.cwporter.com/k1.htm
- Mark Weber. The Nuremberg Trials and the Holocaust. Institute for Historical Review. http://www.ihr.org/jhr/v12/v12p167_Webera.html
- Made in Russia: The Holocaust http://www.ihr.org/jhr/v09/v09p-89_OKeefe.html