Subjects of criminal proceedings as well as other bodies establish the facts, and one of the most important bodies is the law enforcement authorities, i.e. the police. Police duties are performed and police powers are applied by the police according to the Law, and their activities can be divided into formal and informal. Formal is strictly legally regulated and is undertaken exclusively in a manner prescribed by law, while informal is not strictly legally regulated, but must be in accordance with the circumstances of the case and the rules of the profession. An example of informal activity is investigations of criminal offences, which collect information and facts for the decision to initiate criminal proceedings. Formal proceedings include urgent evidentiary actions and special evidentiary actions. Urgent evidentiary actions are performed by the police in cases where there is a risk of delay, and the evidentiary actions that can be taken are search, temporary confiscation of objects, recognition, examination and taking of fingerprints and other body parts. One of the most important evidentiary actions is the investigation, which is the action of observation as a directed observation that can be undertaken in the preliminary procedure, during the investigation and after the indictment has been filed. The procedure for conducting an investigation is insufficiently regulated by law, therefore, in the practice of courts and law enforcement bodies, there are uneven solutions and some open issues are resolved arbitrarily. Investigation is a complex operation that requires teamwork, precision and thoroughness, and the procedure itself is prescribed by criminal science, which plays a major role as a major source of information for investigative bodies.