In criminal proceedings, the establishment of facts beyond reasonable doubt is a cornerstone principle, ensuring that criminal offenses are accurately identified and perpetrators are justly punished while respecting the rights of all parties involved. The proof process is vital, with evidence playing an essential role in determining the outcomes of various procedural stages. Among the types of evidence, expert evidence has become increasingly significant, especially with advances in science and technology broadening the scope of issues requiring specialized knowledge. This paper aims to analyze the roles and impacts of professional and expert activities in criminal procedures. It seeks to highlight the distinctions between expert reports and professional statements, illustrating their respective legal standings and importance in the context of Slovak law. By examining the regulatory framework, specifically Act No. 382/2004 Coll. on experts, interpreters, and translators, and the Criminal Procedure Code (Act No. 301/2005 Coll.), the paper delves into the conditions, rights, and obligations of experts. Additionally, it addresses the significance of expert consultants introduced by the Criminal Procedure Code, who provide advisory services without precluding the involvement of expert witnesses for comprehensive technical assessments. Expert reports, governed by stringent formalities, are pivotal in addressing complex technical issues within criminal cases. These reports must be produced by court-appointed experts and include detailed descriptions of the methods used and the conclusions drawn. Conversely, professional statements, considered documentary evidence, do not carry the same legal weight and lack the formalities required for expert reports. The Criminal Procedure Code also ensures that expert evidence is used appropriately by stipulating when and how expert opinions should be sought. This comprehensive approach ensures that all technical and scientific issues are thoroughly examined, contributing to the fair administration of justice. In conclusion, the integration of expert and professional activities in criminal proceedings enhances the accuracy and reliability of judicial decisions. By leveraging specialized knowledge, the legal system can better fulfill its mandate of delivering justice while upholding the principles of fairness and due process. This paper underscores the necessity of clear regulatory frameworks and the proper application of expert evidence to achieve these aims.