Duquesne was brought to trial and was convicted. He was sentenced to serve 18 years in prison on espionage charges, as well as a 2-year concurrent sentence and payment of a $2,000 fine for violation of the Foreign Agents Registration Act. He served his sentence in Leavenworth Federal Penitentiary in Kansas, where he was mistreated and beaten by other inmates. In 1954 he was released due to ill health, having served 14 years, and died indigent, at City Hospital on Welfare Island (now Roosevelt Island), New York City on May 24, 1956, at the age of 78.