The polygraph examiner may assist the arson investigator by screening suspects, witnesses, informants, and complainants. Suspects are examined by asking them specific questions (e.g., how the fire started) to which only 'yes' or 'no' answers can be given. More detailed questions are asked after the screening process is completed. The questions may concern the identity of the arsonist, the circumstances, and the motive of the crime. The close cooperation between the investigator and the polygraph examiner is essential. For example, accurate information must be given to the polygraph examiner prior to the test since false reactions of the subject will be obtained when false information is given. Since the polygraph technique involves the recording of changes in the physiology of certain bodily systems, the subject's physiology should be normal at the test time (e.g., the subject should not be tired). Frequently, the question is raised as to the advisability of the polygraph since the results may not be used in court. However, the polygraph is useful in helping investigators decide on the right course of action. Cases in which the polygraph helped determine guilt or innocence are described.