According to Oleg Gordievsky, the highest-ranking KGB officer ever to defect, and Pavel Sudoplatov, the former deputy director of Foreign Intelligence for the Soviet Union, Pontecorvo was a Soviet spy. However, Sudoplatov misidentified Pontecorvo as the spy codenamed Mlad, whom we now know was Ted Hall. While Pontecorvo always denied working on nuclear weapons, in Canada, Britain or the Soviet Union, he never confirmed or denied that he was a spy. The actual evidence against him was flimsy. Frank Close noted that the blueprints of the Canadian NRX reactor had made their way to the Soviet Union, and Lona Cohen obtained a sample of uranium from the NRX after it started operation in 1947. Nunn May could not have been the culprit, so Pontecorvo is the prime suspect.