The Prosecutor General’s Office has given Polish authorities 20 additional volumes of documents concerning the Soviet execution of Polish officers at Katyn in 1940, the RIA Novosti news agency reports. In May Moscow sent to Poland 67 volumes of the case. The Polish commission insisted, however, that those volumes did not contain any new information concerning the case.

“We are handing over additional 20 files from case #159, which partly fulfills the Polish request,” senior Russian Prosecutor Saak Karapetyan said. The files contain additional lists of Polish servicemen held captive by the Soviet secret police, interrogation and forensic reports, medical records, burial certificates and other data related to the massacre.

In the 1990s, Russia handed over to Poland copies of archive documents from the top-secret File No.1, which placed the blame solely on the Soviet Union. In September 1990, Russian prosecutors also launched a criminal case into the massacre, known as “Case No.159.” The investigation was closed in 2004.

Poland’s Institute of National Remembrance, which has been investigating the case since 2004, has proposed including Russia’s materials into its own investigation.