 Complete the following phrase:  Lithuania used gas chambers for civilian, penal use in the 1930s, with the last known execution carried out in 1940. The Soviet Union allegedly used the method to perform executions during the bloody Great Purge, including by use of gas vans. Prisoners were gassed on the way to the Butovo firing range, where the NKVD normally executed its prisoners by shooting them. None of these saw mass use, however, and were strictly for criminal purposes. It is unknown to what extent, if any, Lithuanian or Soviet use may have influenced the methods of Nazi Germany 