He became an international spy unconditionally faithful to Stalin, and unlike some of the communist Jewish intellectuals who ran the Comintern at the time, he accepted the German-Soviet Pact and was entrusted with the implementation of secret policies by Stalin's politburo. He was strongly suspected, without conclusive evidence, of involvement as Ramon Mercader's handler in the assassination of Leon Trotsky, and in the supposed murder of Willi Münzenberg who was found hanged in a French forest. Various purges, liquidations and murders required by Stalin during the Spanish Civil War are also attributed to him.
