In the 19th century, Piotr Koźliński married Leokadia Lefftreu, the daughter of the director of the English railway construction company in Russia.

On 5 March 1940, Stalin approved, together with Voroshilov, Mikoyan and Molotov, a proposal from Beria that led to the assassination of 21,857 Poles.

[5] Despite claims by the Poles, the Soviet Union blamed Nazi Germany for the mass murders and attempted to hide its involvement, going as far as to ban all mention of the Katyn massacre in the USSR.

[citation needed] The NKVD resolved to execute prisoners of war and "members of various counter-revolutionary organisations, former landowners, factory owners, former Polish officers, officials and escapees".

[6] The 2007 Polish film Katyń, directed by Andrzej Wajda, is an interpretation of the events that led up to the mass execution.