Stalin orchestrated the arrest of many former opponents in the Communist Party as well as sitting members of the Central Committee: denounced as Western-backed mercenaries, many were imprisoned or exiled internally. The first Moscow Trial took place in August 1936; Kamenev and Zinoviev were among those accused of plotting assassinations, found guilty in a show trial, and executed. The second Moscow Show Trial took place in January 1937, and the third in March 1938, in which Bukharin and Rykov were accused of involvement in the alleged Trotskyite-Zinovievite terrorist plot and sentenced to death. By late 1937, all remnants of collective leadership were gone from the Politburo, which was controlled entirely by Stalin.