One of Saypol's assistants on the prosecution team was Roy Cohn, the son of Judge Albert Cohn of the New York State Supreme Court. Cohn joined the U.S. Attorney's office following law school and had worked with Saypol prior to the Rosenberg case in an trial of eleven Communists.

During the trial, Cohn was noticed by Senator Joseph McCarthy. He later served as an aide to the Senator. Senator McCarthy, of course, became infamous for his accusations of Communist infiltration of the State Department and other high government posts. Cohn provided legal guidance to the Senator in his Communist "witch-hunt" which would become known as "McCarthyism." Eventually Senator McCarthy's influence declined and he, along with Cohn, was discredited.