victims, murdered in 1940 by order of Soviet authorities The Soviet Union never officially declared war on Poland and ceased to recognise the Polish state at the start of the invasion. As the Soviet Union had not signed international conventions on
rules of war, the Polish prisoners were denied legal status. The Soviet forces murdered almost all captured officers, and sent numerous ordinary soldiers to the Soviet
Gulag. In one notorious atrocity ordered by Stalin, the Soviet secret police systematically shot and killed 22,000 Poles in a remote area during the
Katyn massacre. Among some 14,471 victims were top Polish Army officers, including political leaders, government officials, and intellectuals. Some 4,254 dead bodies were uncovered in mass graves in
Katyn Forest by the Nazis in 1943, who invited an international group of neutral representatives and doctors to examine the corpses and confirm the Soviet guilt. but thousands of others were victims of
NKVD massacres of prisoners in mid-1941, before the
German advance across the Soviet occupation zone. In total, the Soviets killed tens of thousands of
Polish prisoners of war. Many of them, like General
Józef Olszyna-Wilczyński, captured, interrogated and shot on 22 September, were killed during the 1939 campaign. On 24 September, 1939, the Soviets killed 42 staff and patients of a Polish military hospital in the village of
Grabowiec, near
Zamość. The Soviets also executed all the Polish officers they captured after the
Battle of Szack, on 28 September. The Soviet authorities regarded service to the prewar Polish state as a "crime against revolution" and "counter-revolutionary activity", and proceeded to arrest large numbers of Polish
intelligentsia, former officials, politicians, civil servants and scientists, intellectuals and the clergy, as well as ordinary people thought to pose a threat to Soviet rule. In the two years between the invasion of Poland and the 1941 attack on USSR by Germany, the Soviets arrested and imprisoned about 500,000 Poles. This was about one in ten of all adult males. The arrested members of the Polish intelligentsia included former prime ministers
Leon Kozłowski and
Aleksander Prystor,
Stanisław Grabski and
Stanisław Głąbiński, and the
Baczewski family. Initially aimed primarily at possible political opponents, by January 1940 the NKVD's campaign was also directed against potential allies, including Polish Communists and Socialists. Those arrested included
Władysław Broniewski,
Aleksander Wat,
Tadeusz Peiper,
Leopold Lewin,
Anatol Stern,
Teodor Parnicki, Marian Czuchnowski and many others. The Soviet NKVD executed about 65,000 imprisoned Poles after being subjected to
show trials. as at least 150,000. According to other scholars, who depart from demographic data and take into account the population Poland lost through post-war citizenship changes, the total figure of Soviet-inflicted Polish deaths in the entire World War II period (1939–1945) probably did not exceed 100,000. ==Mass deportations to the East==