I remember from the book in ‘Enola Gay’ that when they were looking at Oppenheimer they had the wrong guy. The author of the book stated that a scientist named David Greenglass was an actual Soviet spy, passing atomic secrets to the Soviets, not Oppenheimer.
Klaus Fuchs, Ted Hall, David Greenglass, the Rosenbergs, all passed atomic secrets on to the Soviet Union. There was no shortage of Soviet sympathizers and spies in and around the Manhattan Project.