[3] Heilmann's mother had ensured he learned a number of languages and this meant he was selected to be trained as a cryptologist and translator.

[6] At Schulze-Boysen and Haushofer first meeting, also attended by Rainer Hildebrandt whose apartment they were using and another student, discussed the possibility of cooperation between Germany and the Soviet Union.

[6] These two meetings created a level of trust between the two men that reduced their risk of exposure when trying to turn the Wehrmacht officer.

At some point during that year, Heilmann tried to recruit Technical sergeant (German: Wachtmeister) Alfred Traxl but they remained colleagues instead of collaborators.

It was the discovery of the radio transmissions of Johann Wenzel who was captured by the Gestapo on 29–30 June 1942[8] that eventually revealed the members of the anti-fascist group and led to the arrest of Heilmann.

The last message that was deciphered provided three addresses that were passed to the Reich Security Main Office IV 2A who easily identified the people living there, and from 16 July 1942 were put under surveillance.

[10] When Vauck answered he was astonished that the person who was prime subject of his investigation was on the phone and realised that Heilmann was a traitor.