Though the killings also occurred in the Kalinin and Kharkiv NKVD prisons and elsewhere, the massacre is named after the Katyn forest, where some of the mass graves were first discovered by Nazi German forces in 1943.

Since Poland's conscription system required every nonexempt university graduate to become a military reserve officer,[21] the NKVD was able to round up a significant portion of the Polish educated class as prisoners of war.

[33] The head of the NKVD Administration for Affairs of Prisoners of War and Internees, Pyotr Soprunenko [ru], a Major-General born near Kiev in the Ukrainian SSR was involved in "selections" of Polish officers to be executed at Katyn and elsewhere.

[43] Vasily Mikhailovich Blokhin, chief executioner for the NKVD, 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 28 days in April 1940.

[35][44] After the condemned individual's personal information was checked and approved, he was handcuffed and led to a cell insulated with stacks of sandbags along the walls, and a heavy, felt-lined door.

Some post-1991 revelations suggest prisoners were also executed in the same manner at the NKVD headquarters in Smolensk, though judging by the way the corpses were stacked, some captives may have been shot while standing on the edge of the mass graves.

[53] Joseph Goebbels saw this discovery as an excellent tool to drive a wedge between Poland, the Western Allies, and the Soviet Union, and reinforcement for the Nazi propaganda line about the horrors of Bolshevism, and American and British subservience to it.

[66][67] As none of the documents found on the dead had dates later than April 1940, the Soviet secret police planted false evidence to place the apparent time of the massacre in mid-1941, when the German military had controlled the area.

[67] NKVD operatives Vsevolod Merkulov and Sergei Kruglov issued a preliminary report, dated 10–11 January 1944, that concluded the Polish officers were shot by German soldiers.

In retrospective review of records, both British Prime Minister Winston Churchill and U.S. President Franklin D. Roosevelt were increasingly torn between their commitments to their Polish ally and the demands by Stalin and his diplomats.

The report deconstructed the Soviet account of the massacre and alluded to the political consequences within a strongly moral framework but recognized there was no viable alternative to the existing policy.

His efforts were at first highly regarded, but subsequently ignored, which a disillusioned Jeffery later attributed to the actions of Kim Philby and other high-ranking Communist agents entrenched in the British government.

[30] Having consulted with Elmer Davis, director of the United States Office of War Information, Roosevelt rejected the conclusion (officially), declared he was convinced of Nazi Germany's responsibility, and ordered that Earle's report be suppressed.

[75] Documents released by the National Archives and Records Administration in September 2012 revealed Stewart and Van Vliet sent coded messages to their American superiors indicating they saw proof that implicated the Soviets.

[77] During the 1951–52 Congressional investigation into Katyn, Bissell defended his action before the United States Congress, arguing it was not in the U.S. interest to antagonize an ally (the USSR) whose assistance the nation needed against the Empire of Japan.

One of them, Arno Dürre, who was charged with murdering numerous civilians using machine-guns in Soviet villages, confessed to having taken part in the burial (though not the execution) of 15,000 to 20,000 Polish POWs in Katyn.

According to the Committee conclusion: "the Katyn massacre involved some 4,243 of the 15,400 Polish Army officers and intellectual leaders who were captured by the Soviets when Russia invaded Poland in September 1939."

In the late 1970s, democracy groups like the Workers' Defence Committee and the Flying University defied the censorship and discussed the massacre, in the face of arrests, beatings, detentions, and ostracism.

[30] In the Soviet Union during the 1950s, the head of KGB, Alexander Shelepin, proposed and carried out the destruction of many documents related to the Katyn massacre to minimize the chance the truth would be revealed.

On 30 October 1989, Gorbachev allowed a delegation of several hundred Poles, organized by the Polish association Families of Katyń Victims, to visit the Katyn memorial.

[30][99] Among the documents was a proposal by Beria, dated 5 March 1940, to execute 25,700 Poles from Kozelsk, Ostashkov and Starobelsk camps, and from certain prisons of Western Ukraine and Belarus, signed by Stalin (among others).

[35] He further claimed to prosecutors that from late March to late May 1940 he had been in Vyborg and that when he returned to Moscow the prisoners were gone and the NKVD management would not tell him where the Poles had gone, adding that 'in those times it was impossible to ask...'[100] Further testimonies were publicized in October 1991 via a report made by Nicholas Bethell, a British historian and Conservative member of the European Parliament, who obtained videotaped copies of the interrogations to surviving participants, statements, and met with military prosecutors in Moscow.

[103] Earlier in August 1991, Tokarev, who still lived in Miednoje, had reportedly told Colonel Aleksander Tretetsky of the Soviet Prosecutor's Office, the exact location where the Polish remains were.

[114] The plaintiffs filed an appeal but a 21 October 2013 ruling essentially reaffirmed the prior one, claiming that the matter is outside the court's competence, and only rebuking the Russian side for its failure to substantiate adequately why some critical information remained classified.

[120] A civil rights group, Memorial, said the ruling could lead to a court decision to open up secret documents providing details about the killings of thousands of Polish officers.

[112][126][127] In June 1998, Boris Yeltsin and Aleksander Kwaśniewski agreed to construct memorial complexes at Katyn and Mednoye, the two NKVD execution sites on Russian soil.

[citation needed] On 4 February 2010, the Prime Minister of Russia, Vladimir Putin, invited his Polish counterpart, Donald Tusk, to attend a Katyn memorial service in April.

[137] In November 2010, the State Duma (lower house of the Russian parliament) passed a resolution declaring long-classified documents "showed that the Katyn crime was carried out on direct orders of Stalin and other Soviet officials".

[142] In September 2009, Yevgeny Dzhugashvili, Stalin's grandson, sued Russian opposition newspaper Novaya Gazeta after it published an article claiming his grandfather personally signed execution orders against civilians.

[12] On 10 April 2022, in response to Polish authorities demolishing or removing "Soviet occupation monuments", pro-government activists in support of the invasion parked heavy machinery with flags of the Russian Federation and the letter Z outside the Katyn Memorial Cemetery, which was interpreted as an act of intimidation.