When his term of exile ended, in 1942, he was drafted into the Red Army, and took part in the war, but he was arrested again in 1944, and on 10 February 1945 was sentenced to ten years in the Gulag for 'counter-revolutionary propaganda'.
He met the Soviet leader, and was allocated a good apartment in Moscow, and a post in the History Institute of the USSR Academy of Sciences.
He and his friend, Victor Krasin, an economist and former Gulag inmate, formed the Action Group for the Defence of Human Rights in the USSR.
He was also involved in producing the Samizdat publication A Chronicle of Current Events, which was the main contemporary source of information about political repression in the USSR, and he signed protests against the arrests of dissidents such as Andrei Amalrik, Vladimir Bukovsky and many more.
In March 1971, he addressed an Open Letter to the 24th Congress of the Communist Party of the Soviet Union warning against "a dangerous trend towards the restoration of Stalinist methods of government ... and in art literature, historical works and memoirs - towards the rehabilitation of Stalin himself, one of the greatest criminals of the 20th century.
"[9] As well as renouncing their own pasts, he and his friend Krasin, who was arrested in September 1972, gave the KGB a vast amount of information about other political dissidents.
More than 200 people were interrogated about information given by the pair,[10] including Irina Yakir, who refused to follow her father's example and continued to campaign for civil rights.
On 5 September, they gave a televised news conference, to which foreign correspondents were invited, in which both men confessed that their activity had aided the USSR's enemies abroad, and Yakir denounced reports of the Political abuse of psychiatry in the Soviet Union as 'libelous'.