He was incarcerated in Sugamo Prison. Initially, the Japanese believed, because of his Nazi Party membership and German ties, that Sorge had been an "Abwehr" agent. However, the "Abwehr" denied that he had been one of their agents. Under torture, Sorge confessed, but the Soviet Union denied he was a Soviet agent. The Japanese made three overtures to the Soviet Union and offered to trade Sorge for one of their own spies. However, the Soviet Union declined all of the Japanese attempts and maintained that Sorge was unknown to them.