During the Leipzig Trial, several German aviators who had been trained in secret in the Soviet Union had been arrested.

They had been released when, after secret negotiations, the Bulgarian communists Dimitrov, Vasili Tanev and Blagoi Popov tried in Leipzig are allowed to leave for the Soviet Union.

Dmitrov has settled in Moscow, where he is awarded Soviet citizenship.

The massive popularity he enjoys make him an asset of Joseph Stalin's regime, and Dimitrov is appointed General Secretary of the Comintern from 1934.