In 1942, Nelson also became involved in espionage activities, particularly the Manhattan Project: One part of Nelson's task was to gather information on the atomic bomb project. He was seen and overheard meeting with Communist scientists working at the radiation laboratory at Berkeley. Information gleaned from FBI bugging and wiretaps indicated that several had discussed the atomic bomb project with him. Nelson made notes of what the scientists told him regarding their work, and he was subsequently observed passing materials, which the FBI assumed were his notes, to a Soviet intelligence officer operating under diplomatic cover at the USSR's San Francisco consulate." One of the scientists identified was Joseph Weinberg, who worked at the Radiation Laboratory at the University of California. FBI officials bugged Nelson's residence and discovered that Weinberg had delivered "highly secret information regarding experiments being conducted at the Radiation Laboratory, Berkeley, pertaining to the atomic bomb." Investigators reported that Nelson had "delivered this classified information to Soviet consular officer Ivan Ivanov for transmittal to the Soviet Union."