The Stalinists can deny the veracity of personal recollections but we do have a telegram signed by Stalin in 1937 and addressed to Beriya, Shcherbakov, Zhuravliov, Zhdanov, Vyshinskiy, Golyakov and others, which endorses torture to extract confessions. Here is the original Russian text on the website of the Memorial Society. Try hunting it through google translate and do come back if something isn't coherent.