Karl Günter Zimmer (12 July 1911 – 29 February 1988) was a German physicist and radiation biologist, known for his work on the effects of ionizing radiation on DNA. In 1935, he published the major work, Über die Natur der Genmutation und der Genstruktur, with N. V. Timofeev-Resovskij, and Max Delbrück; it was considered to be a major advance in understanding the nature of gene mutation and gene structure. In 1945, he was sent to the Soviet Union to work on their atomic bomb project. In 1955, he left Russia and eventually went to West Germany. Education Zimmer obtained his doctorate in 1934 with a thesis on photochemistry. Career In Germany Early on, Zimmer worked as an advisor in radiotherapeutic physics in a radiological hospital and as an employee of Auergesellschaft in Berlin. However, he completed most of his theoretical work at the Kaiser-Wilhelm Gesellschaft's Institut für Hirnforschung (KWIH, Kaiser Wilhelm Institute for Brain Research) in Berlin-Buch. Zimmer worked in N. V. Timofeev-Resovskij's Genetics Department at the KWIH. Timofeev-Resovskij, a citizen of the Soviet Union, worked in Germany starting in 1924, and he stayed even after Adolf Hitler came to power in 1933. Very early in Zimmer's career, in 1935, he published the major work, Über die Natur der Genmutation und der Genstruktur, with Timofeev-Resovskij, and Max Delbrück; it was considered to be a major advance in understanding the nature of gene mutation and gene structure. At Auergesellschaft, Zimmer collaborated with Nikolaus Riehl, director of scientific research at the works. At the close of World War II, Russia had special search teams operating in Austria and Germany, especially in Berlin, to identify and "requisition" equipment, materiel, intellectual property, and personnel useful to the Soviet atomic bomb project. The exploitation teams were under the Russian Alsos and they were headed by Lavrenij Beria's deputy, Colonel General A. P. Zavenyagin. These teams were composed of scientific staff members, in NKVD officer's uniforms, from the bomb project's only laboratory, Laboratory No. 2, in Moscow. In mid-May 1945, the Russian nuclear physicists Georgy Flerov and Lev Artsimovich, in NKVD colonel's uniforms, compelled Zimmer to take them to the location of Riehl and his staff, who had evacuated their Auergesellschaft facilities and were west of Berlin, hoping to be in an area occupied by the American or British military forces. Riehl was detained at the search team's facility in Berlin-Friedrichshagen for a week. This sojourn