The author of the study supports the scientists' standpoint on the presence of evidence of non-public investigation actions in the activities of an investigator and believes that under modern circumstances the effective investigation of crimes is simply impossible without non-public investigative criminal proceedings. Moreover, non-public investigation action means all activities in a criminal case (investigative actions and criminal procedure) which have the signs of secrecy and confidentiality. Given these signs of non-public investigative criminal proceedings the author suggests his own classification of the acts in question; besides, some common signs of non-public investigating and investigative actions and decisions are disclosed. While dividing non-public investigating activities in criminal cases into relatively and absolutely non-public, the author classifies non-public investigative activities and making non-public decisions according to the degree and purposes of non-publicity as absolutely non-public, relatively non-public and confidential. To sum up, the author dwells upon the need to revise current legal doctrines in terms of integration of investigating and criminal procedure.