 In that same year, Schulze-Boysen had access to other resistance groups and had started to cooperate with them.The most important of these was a group run by Arvid Harnack who had known Schulze-Boysen since 1935  but been reintroduced to him sometime in late 1939 or early 1940 through Greta Kuckhoff.Kuckhoff knew Arvid and Mildred Harnack when she was studying in America at the end of the twenties and had brought the poet Adam Kuckhoff together with the couple.