The European Court of Human Rights (ECHR) says it will not examine the thoroughness of a Russian investigation into the massacre of Polish war prisoners in 1940.
The infamous incident in the Katyn area, which left over 20,000 dead at the hands of the Soviet secret police, led to a bitter international dispute.
In 1944, a Soviet commission accused German soldiers of the executions and only accepted the blame in 1990.
According to a declassified KGB memorandum, the order came from Soviet Communist Party leaders.
Although the ECHR said Russia had kept key files secret, it also said that it had no authority because too much time had elapsed between the killings and the introduction of the European Convention on Human Rights.
In an attempt at reconciliation, former Russian Prime Minister Vladimir Putin and his Polish counterpart Donald Tusk met in 2010 to commemorate the victims. To date, nobody has ever been convicted for the atrocity.