Thousands of Polish army officers were captured by the Soviet Red army in 1939 and were sent to prison camps near Smolensk Russia. Once the Germans invaded the Soviet Union in 1941 (breaking their “Non-Aggression Pact”), the British and the Soviets became allies. The Brits wanted the pro-Western Polish government in exile (stationed in London) to form an army to fight the Germans. Stalin and his Soviet army agreed to release Polish prisoners to begin forming that army.
However, the Polish government in exile noticed that thousands of Polish officers were not being released. When pressed by the Polish government, Stalin said that they had escaped from Soviet camps and were probably somewhere in Manchuria.
In 1943 the Germans released the news that their army had discovered mass graves of thousands of Polish army officers near the Katyn Forest near Smolensk. The dead officers were all wearing heavy winter clothing and were all shot in the back of the head. The Germans blamed the Soviet NKVD (the communist secret police of the USSR). The Soviets said they were all shot by the Germans.
The truth was finally confirmed after the collapse of the Soviet Union in 1991. Once the files of the KGB (successor to the NKVD) were opened, the Russian government admitted that they had murdered some 22,000 Polish army officers as well as civilians in April of 1940. Half the Polish army officer corps had been executed. The victims were also the intelligentsia of Polish society: university professors, schoolteachers, industrialists, clergy (both Catholic and Jewish), inventors, artists, musicians, journalists…pretty much anyone with “higher education” or in leadership was a target of Stalin. He personally ordered their murder. He did not want anyone in Poland who could possibly be a threat to his puppet communist government later installed by his secret police.
So they were all shot. But the truth always comes out.
And freedom eventually wins.
Today Poland is free.