Cohn is best known for his role in prosecuting suspected communists during the Second Red Scare in the early 1950s.

He served as a prosecutor of Julius and Ethel Rosenberg, a Jewish couple accused of unlawfully providing American military and nuclear secrets to the Soviet Union.

• He played a major role in assisting Senator Joseph McCarthy's investigation of suspected communists.

• During the 1970s and 80s, he rose to prominence in New York City, and represeted Donald Trump during his early business career.