The Serpent(1973)

Original title: Le Serpent

Vlassov is a Soviet spy who defects in France. He is whisked to the U.S, where Allan Davies takes over the case. After polygraph tests and cross-examinations, Vlassov names several Western European agents who are also spying for the Soviets. Davies wants to take the listed agents into custody; meanwhile, those on the list start dying under mysterious circumstances.