 Complete the following phrase:  Following the Operation Barbarossa, the Germans and German-held Polish forced laborers discovered the mass graves of over 4,000 Polish officers and intelligentsia murdered in the Katyn Forest by the Soviet Union in 1940. In April 1943, Germany exposed the crime, now known as the Katyn massacre, to the world. The Germans allowed the International Red Cross and Polish Red Cross to the site, and formed the 