TY JOUR TI Constitutional right to receive qualified legal assistance in operational investigative activities KW lawyer KW principal KW constitutional rights and freedoms KW prosecution KW defense KW operative investigation measures JO Vestnik of the St. Petersburg University of the Ministry of Internal Affairs of Russia AU Gusev, V.A. AU Larin, E.G. PY 2021 IS 2021 PB SAINT-PETERSBURG UNIVERSITY OF THE MINISTRY OF INTERNAL AFFAIRS OF THE RUSSIAN FEDERATION