According to a report from 19 November 1939, the NKVD had about 40,000 Polish POWs: about 8,000–8,500 officers and warrant officers, 6,000–6,500 police officers, and 25,000 soldiers and non-commissioned officers who were still being held as POWs.[1][13][22] In December, a wave of arrests resulted in the imprisonment of additional Polish officers. Ivan Serov reported to Lavrentiy Beria on 3 December that "in all, 1,057 former officers of the Polish Army had been arrested".[10] The 25,000 soldiers and non-commissioned officers were assigned to forced labor (road construction, heavy metallurgy).[10]
Once at the camps, from October 1939 to February 1940, the Poles were subjected to lengthy interrogations and constant political agitation by NKVD officers such as Vasily Zarubin. The prisoners assumed that they would be released soon, but the interviews were in effect a selection process to determine who would live and who would die.[23][24] According to NKVD reports, if the prisoners could not be induced to adopt a pro-Soviet attitude, they were declared "hardened and uncompromising enemies of Soviet authority".[23]
On 5 March 1940, pursuant to a note to Joseph Stalin from Beria, four members of the Soviet Politburo—Stalin, Vyacheslav Molotov, Kliment Voroshilov, and Anastas Mikoyan—signed an order to execute 25,700 Polish "nationalists and counterrevolutionaries" kept at camps and prisons in occupied western Ukraine and Belarus.[25][c] The reason for the massacre, according to historian Gerhard Weinberg, was that Stalin wanted to deprive a potential future Polish military of a large portion of its talent:
"It has been suggested that the motive for this terrible step [the Katyn massacre] was to reassure the Germans as to the reality of Soviet anti-Polish policy. This explanation is completely unconvincing in view of the care with which the Soviet regime kept the massacre secret from the very German government it was supposed to impress. ... A more likely explanation is that ... [the massacre] should be seen as looking forward to a future in which there might again be a Poland on the Soviet Union's western border. Since he intended to keep the eastern portion of the country in any case, Stalin could be certain that any revived Poland would be unfriendly. Under those circumstances, depriving it of a large proportion of its military and technical elite would make it weaker".[26]
In addition, Soviets realized that the prisoners constituted a large body of trained and motivated Poles who would not accept a Fourth Partition of Poland.[1]
The number of victims is estimated at about 22,000, with a lower limit of confirmed dead of 21,768.[1] According to Soviet documents declassified in 1990, 21,857 Polish internees and prisoners were executed after 3 April 1940: 14,552 prisoners of war (most or all of them from the three camps) and 7,305 prisoners in western parts of the Byelorussian and Ukrainian SSRs.[27] Of them 4,421 were from Kozelsk, 3,820 from Starobelsk, 6,311 from Ostashkov, and 7,305 from Byelorussian and Ukrainian prisons.[27] Head of the NKVD POW department, Maj. General P. K. Soprunenko, organized "selections" of Polish officers to be massacred at Katyn and elsewhere.[28]
Detailed information on the executions in the Kalinin NKVD prison was provided during a hearing by Dmitrii Tokarev, former head of the Board of the District NKVD in Kalinin. According to Tokarev, the shooting started in the evening and ended at dawn. The first transport on 4 April 1940, carried 390 people, and the executioners had difficulty killing so many people in one night. The following transports held no more than 250 people. The executions were usually performed with German-made 7.65×17mm Walther PPK pistols supplied by Moscow, but 7.62×38mmR Nagant M1895 revolvers were also used.[31] The executioners used German weapons rather than the standard Soviet revolvers, as the latter were said to offer too much recoil, which made shooting painful after the first dozen executions.[32] Vasili Mikhailovich Blokhin, chief executioner for the NKVD—and quite possibly the most prolific executioner in history—is reported to have personally shot and killed 7,000 of the condemned, some as young as 18, from the Ostashkov camp at Kalinin prison over a period of 28 days in April 1940
