He reached the rank of lieutenant-colonel. He assassinated Tetsuzan Nagata with his sword on August 12, 1935, because he was reputedly putting the Army "in the paws of high finance". Aizawa made no attempt to resist arrest and reportedly said that he "was in an absolute sphere, so there was neither affirmation nor negation, neither good nor evil". After a high-profile trial, he was executed by a firing squad. His actions helped the Tōseiha faction, which he hated, gain absolute control over the Japanese military.