1. The Katyn tragedy involved Stalin, so the Soviet Union did not destroy the archives: during World War II, some things in the Soviet Union were unacceptable, and these things even exposed some dark sides of the Soviet Union. In the years before the Second World War, Europe had been restless, and the contradiction between the Soviet Union and Poland became more acute, so the Katyn tragedy appeared later. 1943 The Germans found the bodies of tens of thousands of dead people, and at that time they accused the Soviet Union of its actions, but at that time the Soviet Union directly and completely denied it. This incident caused a lot of controversy at that time, but during World War II, everyone United against the Germans, so we didn't pursue this matter further. This matter is actually directly related to Stalin. Later, after Stalin's death, the Soviet government thoroughly criticized Stalin, so this important file was preserved.
Second, the United States also participated, so the Soviet Union did not destroy the documents:
The archives of the Katyn massacre can be preserved later, in fact, there are some reasons in the United States. In fact, the Katyn tragedy can be avoided, because if the United States can improve the testimony of prisoners in those years, Stalin of the Soviet Union will not make a decisive decision. However, as the president of the United States, Roosevelt hoped to provoke the Soviet Union to participate in the war against Germany through the Katyn massacre, so he would hide a lot of things, and therefore the Soviet high-level officials would keep this information.
Third, there is a lot of direct evidence about the Katyn tragedy, and it is meaningless to destroy the archives:
Another main reason is that the Katyn tragedy attracted the attention of many people in Europe at that time, and their investigation was very in-depth, especially some historians in Poland, who had a lot of evidence, so it was of little significance for the Soviet Union to destroy archives. Therefore, the Soviet high-level integrated the above factors and did not destroy the archives of the Katyn massacre.