Over 20,000 Polish military officers, police and civilians taken prisoner during the 1939 partitioning of Poland by the Soviet Union and Nazi Germany were massacred in the Katyn forest, as well as in prisons and other locations, by the NKVD, the forerunner of the KGB.
Anna Stavitskaya, a lawyer for the families of those killed, told RIA Novosti she would appeal the military court's ruling in a higher court.
In 2005, the Chief Military Prosecutor's Office closed the "Katyn Case" saying there was no evidence of genocide against the Polish people, and that those involved in the executions had since died. However, the relatives of the executed officers appealed the decision to close the case.
The Soviet Union initially accused Germany of executing the Polish prisoners. However, in 1990 Mikhail Gorbachev officially admitted that Soviet secret police were responsible for the massacre.
Russian prosecutors earlier put the number of those killed at 14,500.