According to Professor Wojciech Materski, a German-Soviet training center for security forces was established in Zakopane, Poland, in December 1939, but no documents on this cooperation have been found to date; see KDZ1, p. 18. According to another Polish historian, cooperation against Polish independence movements began with a meeting of NKVD and SS officers in Lviv [Lwów] in October 1939, followed by meetings in Zakopane in December 1939 and Kraków in March 1940; see Piotr Kolakowski, NKWD i GRU na Ziemiach Polskich, 1939–1945 [The NKVD and GRU on Polish Territories, 1939–1945] (Warsaw, 2002), pp. 66–67.