In 1943 Coplon, a 21-year-old graduate of Barnard College, joined the Department of Justice in New York; two years later she transferred to headquarters in Washington, D.C. In 1948 she was identified as the spy code-named SIMA in the VENONA traffic, and the Federal Bureau of Investigation placed her under surveillance. Her office telephone was tapped, and she was arrested as she met her Soviet contact, Valentin Gubitchev, in New York.
Coplon’s subsequent conviction of theft of government documents was quashed on appeal because she had been arrested without a warrant and because the wiretap evidence had not been disclosed to the defense. When the VENONA traffic was declassified, it became clear that the FBI had been anxious to conceal the true nature of the original lead that had prompted the investigation. An employee of the United Nations, Gubitchev was deported from the United States, but Coplon was freed and later married her lawyer. Although the conviction was set aside, the Coplon case was an important milestone in the development of VENONA and acted as the catalyst for Congress to pass a law allowing warrantless arrests to be made where espionage is alleged.