Perseus reportedly introduced himself to Cohen as a physicist who had been invited to join the work at Los Alamos research center. By 1942, Perseus was supposedly already working at Los Alamos, being that he would have started sometime at least 18 months before German physicist and also atomic spy Klaus Fuchs, who joined the investigation in mid-1944. However, Perseus appears to have been recruited by the Soviets around the same (or at least a nearby) time as Fuchs.