According to Poland's criminal law, the Code of Criminal Procedure, an expert witness should be sought when specialized knowledge about the material facts of the case would have a vital bearing on the case's resolution. Expert witnesses are given examinations to demonstrate their expertise in a particular field. They examine a set of facts and phenomenon to determine the reasons why an incident occurred. By taking into consideration all the evidence the court provides and by estimating the degree of probability about a defendant's involvement in the crime, expert witnesses use principles of logic in determining the merits of each case. They also assist the state in efforts to deter future crime. Expert witnesses may be from a variety of professions and occupations, including medicine, psychology, forensic science, and even shoemaking and house painting if the case warrants it. The primary criterion is that the expert witness have the knowledge, technical skills, and specialized training and experience in a field whose body of knowledge has a bearing on the case. A procedural decision designates the type of expert witness needed in a given case. The expert witness must be appointed by the legal organ that is conducting the investigation, i.e., the public prosecutor or the police during preparatory proceedings and the court during the trial. Expert witnesses must pledge themselves to impartiality in the case. 18 notes