The paper analyzes the errors committed by law enforcement officers in the implementation of various types of special knowledge at all stages of criminal proceedings. Shortcomings under consideration are differentiated into shortcomings committed in the production of investigative actions, during which objects were seized, subsequently presented for an expert examination, when forensic examinations are appointed, in the production of forensic examinations, when examining the expert's opinion by officials of the preliminary investigation bodies and the prosecutor's office. At the same time, such errors are periodically repeated and multiply: forensic examinations, the need for the production of which is caused by the specifics of the crime being investigated, the current investigative situation and, being justified by specially developed recommendations, are not scheduled; the questions posed to the experts do not cover all the circumstances the establishment of which is possible only through the involvement of persons knowledgeable in a particular area of special knowledge; the questions themselves are not always directly related to the expert's specialization and the type of examination; the presence of proper qualifications of a person involved as an expert is not verified, etc.

Without setting themselves the task of analyzing all or most of these errors, the authors thoroughly consider the most serious errors using specific examples from judicial investigative practice and they come to the conclusion that the effectiveness and efficiency of using the expert's conclusion in proving is possible only under the context of impeccable observance by officials of preliminary investigation bodies, forensic experts and heads of forensic institutions of the provisions of the Criminal Procedure Law, the Federal Law "On State Forensic Expert Activity", departmental regulations and forensic recommendations.