[3] Heinz Günther Joachim was born in Berlin a few months after the end of the First World War, the first-born of his parents' five sons.

The three friends were all Jewish, and during 1940 they were sent as "forced labourers" to work at the vast Siemens electro-engineering plant ("Siemens-Elektromotorenwerk") in Berlin-Spandau.

At around the time of their marriage Heinz and Marianne Joachim became members of what came to be known as the Baum group, a circle of forced labourers living in Berlin.

Some members were living "underground" – unregistered with any town hall – in order to make it harder for the authorities to track them.

[6] The Baum group's most highly publicised political action was an arson attack carried out on 18 May 1942 against the "Soviet Paradise" exhibition in Berlin's "Lustgarten" pleasure park.

[6] The objective of the exhibition was to demonstrate to the people the "poverty, misery, depravity and need" that were features of life in the "Jewish Bolshevist Soviet Union".

[7] The arson attack inflicted relatively little physical damage on the exhibition, which re-opened the next day, but news of it had a more lasting impact.

[10] Alfons Joachim, the father of Heinz, was the subject of a denunciation in July 1944: he is known to have died on 4 December 1944 at the Sachsenhausen concentration camp.