candidate: Following the fall of the NKVD head , Nikolai Yezhov , the new chief Lavrenti Beria chose to retry Korolev on reduced charges in 1939 , but by that time Korolev was on his way from prison to a gulag camp in the far east of Siberia , where he spent several months in a gold mine in the Kolyma area before word reached him of his retrial .