On this day, 73 years ago, NKVD leader Levitiy Beria signed a document. It was his personal recommendation to the Politburo in Moscow that all Polish officers should be executed.
The recommendation came after the Soviet invasion of Poland in September 1939. Part of the Molotov-Ribbentrof agreement gave half of the nation to Russia along with various other territories. The exact reasons for ordering the executions remains unclear, but there are two probabilities: 1) Stalin knew that Poland would become a nation again one day. As such, it must be deprived of all persons who would fight for her independence. 2) Stalin wanted to present the deaths as a type of gift to Hitler.
The orders were carried out from April to May of the same year. Civilians were also killed, namely those of the Polish intelligentsia. This could include everyone from lawyers, doctors, factory owners, police officers, teachers and priests.
The massacre is often named "Katyn" because the mass execution of military officers took place there. However, there were many different sites used. Katyn became infamous because it was the largest execution of military prisoners in the entire war.
The Nazis excavated the mass graves and invited international reporters to document their findings. These observers included American, British and Canadian military personnel. Stalin denied any involvement, and despite protests from the Polish government in exile, the Allies never brought it up. Stalin went so far as to orchestrate Soviet excavations at the same spot in an attempt to blame it on the Germans.
It wouldn't be until 2010 that the Russian government made an official proclamation blaming Stalin and other Soviet leaders for arranging and ordering the executions. The total number of deaths is slated around 22,000.