In 1948, Whitaker Chambers-- former member of the Communist Party and a Time magazine editor-- accused former State Department official Alger Hiss of being a communist and a spy for the Soviet Union. The accusation set into motion a series of events that eventually resulted in the trial and conviction of Hiss for perjury.
(From: http://www.history.com/this-day-in-history/chambers-accuses-hiss-of-being-a-communist-spy)