The Katyn Forest Massacre took place in the spring of 1940, near what today is Smalensk, Russia; a region that through the early 20th century was a historical Belarusian ethnic area. After WWI, this area became part of Russia. About 4,500 reservist officers were executed (massacred) by the Soviets and quickly buried. The German Army discovered the massacre site during WWII, and the Nazis used this information for propaganda in 1943. The Soviets did not admit to their role in this tragedy until 1990.
There is considerable information about this horrendous tragedy on the Internet, in novels and the movies (see Enigma), etc. For a starting point, refer to the Wikipedia entry.
"As many as 1,059 of the 4,421 the Polish army officers executed by the Soviets in the Katyn forest near Smolensk in western Russia in 1940 were Belarusians, historian Ihar Kuzniatsou (Igor Kuznyetzov) said during a round-table discussion in Minsk on December 11 [2009].
If Jews and Poles from western Belarus are added to this number, about 2,000 people from Belarus were executed in Katyn, Mr. Kuzniatsou said.
The executions of the Polish officers and the annexation of Estonia, Latvia and Lithuania to the Soviet Union will be the two tragic dates whose 70th anniversary will be commemorated in Belarus in 2010, he said.
Although the Germans caused the Poles more harm during World War II than the Russians, there are more grudges in Poland today against the former because they have not repented of their crimes, said Aleh Latyshonak (Oleg Latyszonek), a professor at the University of Bialystok, Poland.
Russia insists that the Red Army was a liberation force, while the Poles viewed both the Soviets and the Nazis as occupiers, he said.
The officers executed in Katyn were among Polish army reservists who were called up for active service following the Nazi invasion of Poland in 1939.
But instead of fighting the Germans, about 15,000 Polish officers found themselves prisoners of the Red Army, which had occupied western Belarus under the terms of a secret Moscow-Berlin treaty.
In the spring of 1940, about 4,500 of those officers were taken by their Soviet captors to the Katyn forest. Most were then gagged, bound, shot once in the head and buried on the spot. The other Polish prisoners of war were taken to other locations, where many of them were also executed."
Source: Naviny/BelaPAN, 15.12.09 // 12:49