Introduction. The article continues the research on revealing the ‘black boxes’ that are modelled in the course of the methodological study of the ‘mechanism of proving criminal activity’. The author puts forward and tests hypotheses concerning the representation of the functional system ‘proving criminal activity’ through its models, and their elements – as ‘inputs’ and ‘outputs’ in the ‘black box’. The author believes that setting regular relations between the structural elements of the models of the mechanism of proving, as well as between ‘inputs’ and ‘outputs’ will allow to understand the examined functional system. Methods. The purpose and tasks of the research, as well as the hypotheses, determined the research programme. The process of their verification was accompanied by the application of dualistic and mechanistic methods, systemactivity approach, methods of functional systems and ‘black box’, structuralfunctional approach, as well as analysis and synthesis, abstraction and concretisation, modelling, forecasting and others. Results. The author has established that the actual activity of proving is a complexfunctional system and it is beyond comprehension. Modelling of this activity makes it possible to present it in a simplified and accessible form, therefore, to talk about its mechanism. The study proved that models help to visualise the structure of the evidence mechanism, as well as reality itself, due to their isomorphism. Furthermore, the study confirmed that the ‘black box’ method allows ones to move sequentially from an incomprehensible functional system to models and then to the mechanism, and that the system-forming elements of the functional system act as ‘inputs’ and ‘outputs’ of the ‘black box’. We found it is precisely the influence on the ‘inputs’ and the observation of changes in the ‘outputs’ that makes it possible to establish pattern relationships in the ‘black box’ and to make the model and reality clear.