The aim of the article is to analyse the Soviet definition of crime, the structure and logic of Soviet criminal law, and the system of criminal prosecution developed by the Bolsheviks after the October Revolution of 1917, consolidated during the NEP and collectivisation, and reformed by Stalin and Andrey Vyshinsky in the mid-1930s. The research also examines the impact that these concepts, ideas, institutions, legal norms and practices had on newly occupied Soviet colonies, focusing on the case of the LSSR. First of all, the research demonstrates that the main laws, institutions and actors in the Soviet criminal justice system which functioned until the mid-1950s without radical changes were invented and defined just after the Revolution, Civil War and NEP. Impacted by Marxist philosophy, by the traditional Russian peasant mentality and pre-revolutionary Bolshevik experiences, the early Bolshevik criminal justice system already had features which became crucial to the implementation of Stalinist mass repressions. For instance, the criminal code of the RSFSR defined a crime as any act or omission dangerous to the Soviet order and state, but not as an act or omission prohibited by law – this was possible due to the ‘principle of analogy’. The criminal code of 1926, based on Bolshevik legal norms from the period of the Revolution and the Russian Civil War, was not replaced during the legal reform of the mid-1930s. The very same system was transferred to the Lithuanian SSR after the occupation. Despite some institutional differences, the main features did not vary from that of the RSFSR, and the two were linked in the common system, the Russian one having hierarchical superiority. ‘Union’ laws prevailed over republican ones. But in the LSSR, the process of colonisation in the field of the criminal justice system was difficult, due to the strong armed anti-Soviet resistance, and the lack of well-educated and loyal Soviet legal personnel.