Joseph Stalin had Theremin imprisoned at the Butyrka in Moscow; he later came to work in the Kolyma gold mines. Although rumors of his execution circulated widely, Theremin was, in fact, put to work in a sharashka (a secret research-laboratory), together with other scientists and engineers, including aircraft designer Andrei Tupolev and rocket scientist Sergei Korolyov (also a Kolyma inmate). The Soviet Union rehabilitated Theremin in 1956. The Kolyma camps switched to using (mostly) free labor after 1954, and in 1956 Nikita Khrushchev ordered a general amnesty that freed many prisoners. Various estimates have put the Kolyma death-toll from 1930 to the mid 1950s between 250,000 and over a million people. Dalstroy was the agency created to manage exploitation of the Kolyma area, based principally on the use of forced labour. In the words of Azerbaijani prisoner Ayyub Baghirov, "The entire administration of the Dalstroy – economic, administrative, physical and political—was in the hands of one person who was invested with many rights and privileges." The officials in charge of Dalstroy, i.e., the Kolyma Gulag camps were:  Calendar of events:  The Chukot Autonomous Okrug site provides details of developments after the official closure of the camps. In 1953, the Magadan Oblast (or region) was established. Dalstroy was transferred to the jurisdiction of the Ministry of Metallurgy and later to the Ministry of Non-Ferrous Metallurgy. Industrial gold-mining started in 1958 leading to the development of mining settlements, industrial enterprises, power plants, hydro-electric dams, power transmission lines and improved roads. By the 1960s, the region's population exceeded 100,000. With the dissolution of Dalstroy, the Soviets adopted new labor policies. While the prison labor was still important, it mainly consisted of common criminals. New manpower was recruited from all Soviet nationalities on a voluntary basis, to make up for the sudden lack of political prisoners. Young men and women were lured to the frontier land of Kolyma with the promise of high earnings and better living. But many decided to leave. The region's prosperity suffered under Soviet liberal policies in the end of the 1980s and 1990s with a considerable reduction in population, apparently by 40% in Magadan. A U.S. report from the late 1990s gives details of the region's economic shortfall citing outdated equipment, bankruptcies of local companies and lack of central support.