Original sentence: In the course of the massacre approximately 22,000 Polish citizens were executed in three mass murder sites in the spring of 1940, according to the view that the Soviets were responsible; another view is that the Germans killed the Poles after invading the Soviet Union in mid-1941, and that the accusation of Soviet guilt was the work of Nazi propaganda.The Katyń Incident, known in Poland as the Katyn Forest Massacre, was a disputed occurrence resulting in the mass execution of Polish citizens during World War II, believed by some to have been perpetrated by the Soviets
Edited sentence: In the course of the massacre approximately 22,000 Polish citizens were executed in three mass murder sites in the spring of 1940.The Katyń Incident, known in Poland as the Katyn Forest Massacre, was a disputed occurence resulting in the mass execution of Polish citizens during World War II, believed by some to have been perpetrated by the Soviets