Some sources claim the massacre was instigated by the Soviet-backed Communist security corps, for propaganda purposes, attempting to discredit Poland's anti-Communist stance and to maintain totalitarian control over the country. As the top-secret case files were destroyed, the academic inquiry is ongoing with regard to possible secret coordination with the NKVD by the Moscow-Communist-controlled 'Polish' authorities. There has been considerable controversy over possible outside incitement. The idea that the event was secretly provoked or inspired by Soviet intelligence services has been put forward, and a number of similar scenarios were offered. None has yet been proven by the post-communist investigation, due to the paper trail (see below) having been destroyed by Communist-controlled intelligence agents, even though an NKVD officer was present at the riots. In 2001–04 the Institute of National Remembrance (IPN) conducted an investigation into the pogrom and closed the case stating (without entering into details) that the events of 4 July 1946 were a result of a mishap. Another communiqué published by the IPN two years later confirmed only that four decades after the fact the remaining paper trail was still being destroyed by the Soviet controlled Polish security police under Gen. Czesław Kiszczak.