Horst Heilmann

This wasn't the first meeting between Schulze-Boysen and Haushofer but was perhaps the first political meeting. According to new evidence that was presented in 2010 Schulze-Boysen and Haushofer met at least twice before, and understood each other's motives, and allowed a compromise to be reached, that in turn enabled the turning of Heilmann away from Nazism. 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. At a second meeting, with trust established between two sides, Haushofer was known to tell Schulze-Boysen that an assassination attempt against Hitler was being planned. 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.

It was the discovery of the radio transmissions of Johann Wenzel who was captured by the Gestapo on 29–30 June 1942 that eventually revealed the members of the anti-fascist group and led to the arrest of Heilmann. When he was captured Wenzel decided to collaborate with the Funkabwehr and it was his exposure of the Wireless Telegraphy codes that enabled the Funkabwehr and specifically Referat 12 to decipher Red Orchestra message traffic. When Heilmann discovered that the Red Orchestra traffic was being read from documents that had been illegally provided by Alfred Traxl, he conducted a search for the names of Kuckoff, Schulze-Boysen and Harnack at the agency and to his horror after 2 days, he discovered that his friends had already been exposed to the Gestapo. According to one version of events Heilmann immediately phoned Schulze-Boysen, using Wilhelm Vauck's office phone that was next door to Heilmann office, as his phone was in use. As Schulze-Boysen wasn't in, Heilmann left a message with the maid of the household. When Schulze-Boysen returned, he immediately phoned the number, but unfortunately, it was answered by Vauck, who was Director of Referat 12. Vauck using the codes that Wenzel provided was able to captured and decipher over 200 radio messages that the Red Orchestra group had sent. 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. 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. He asked Schulze-Boysen to clarify his name to confirm it was spelt with a y or an i. After the call, Vauck phoned the Gestapo and this started a process on 31 August 1942 that resulted in many people of the Red Orchestra being arrested, including Heilmann himself who was arrested on 5 September 1942.

On 19 December 1942, the Reichskriegsgericht sentenced Heilmann to death. On 22 December 1942, Heilmann was executed at Plötzensee Prison by hanging.

In August 1941, after a weekend sailing on the Großer Wannsee, on Schulze-Boysen's boat, the Duschika, Schulze-Boysen confided in Heilmann that he was working for the Russians as an agent.

In 1940 Heilmann met Harro Schulze-Boysen when Heilman wrote a paper called The Soviets and Versailles that was presented at a political seminar for the Hitler Youth at the Deutsche Hochschule für Politik, where Schulze-Boysen was lecturing from September 1940. It was through Schulze-Boysen that Heilmann was introduced to Albrecht Haushofer, the German geographer, diplomat and later professor at the Faculty for Foreign Studies that had moved to the Humboldt University of Berlin and German resistance fighter who was also teaching at the seminar. Heilmann became a pupil of Haushofer.

Heilmann's father was Halle city architect Jakob Adolf Heilmann, and his mother was Helene Heilmann. Heilmann joined the Hitler Youth in 1937 and the Nazi Party in 1941. Heilmann was a student of Federal Foreign Office in Berlin until his conscription in the Wehrmacht. Heilmann mother had ensured he learned a number of languages and this meant he was selected to be trained as a cryptologist and translator. After training, he was posted to the Inspectorate 7/VI, where he worked in Referat 7 and later Referat 1 before being posted to work at the Agents Referat, that later became Referat 12. At the Referat Heilmann worked on the desk that deciphered English, French and Russian intercept traffic.

Horst Heilmann (15 April 1923 – 22 December 1942) was a German resistance fighter against the Nazi regime. He was a member of the anti-fascist resistance group that formed around Harro Schulze-Boysen. This group and many others were bundled together and later called the Red Orchestra by the Abwehr. Heilmann was also a student and a wireless operator who worked at the Referat 12 that was in the Inspectorate 7/VI.