When did the campaign of political  repression that Mikhail Demichev was arrested during occur?
Great Purge The Great Purge or the Great Terror (Russian: Большо́й терро́р ) was a campaign of political repression in the Soviet Union which occurred from 1936 to 1938. It involved a large-scale purge of the Communist Party and government officials, repression of peasants and the Red Army leadership, widespread police surveillance, suspicion of "saboteurs", "counter-revolutionaries", imprisonment, and arbitrary executions. Mobile gas vans were invented to execute people without trial. In Russian historiography, the period of the most intense purge, 1937–1938, is called Yezhovshchina (Russian: Ежовщина ; literally, "Yezhov phenomenon", commonly translated as "times of Yezhov" or "doings of Yezhov"), after Nikolai Yezhov, the head of the Soviet secret police, the NKVD, who was later killed in the purge. It has been estimated that 600,000 people died at the hands of the Soviet government during the Purge.
Dymshits–Kuznetsov hijacking affair The Dymshits–Kuznetsov aircraft hijacking affair, also known as The First Leningrad Trial or Operation Wedding (Russian: Ленинградское самолётное дело , or Дело группы Дымшица-Кузнецова) (Leningrad Process), was an attempt to steal a civilian aircraft on 15 June 1970 by a group of 16 Soviet refuseniks in order to escape to the West. Even though the attempt was unsuccessful, it was a notable event in the course of the Cold War because it drew international attention to human rights violations in the USSR and resulted in the temporary loosening of emigration restrictions.