Denis Trokhin was the Soviet ambassador to Germany during the Weimar era and the Cheka chief in Berlin. In April 1929, he arranged the extermination of a Trotskyist cell, the Red Fortress, in Koepenick, with the help of double agent Svetlana Sorokina. However, he failed to kill the cell's leader Alexei Kardakov, and the accidental explosion of a Soviet train carrying poison gas at the Anhalter train depot implicated the Soviets in smuggling illegal weapons to the Black Reichswehr.