A crucial element in the prosecution of any criminal case is the establishment of the corpus delecti, which means that the fact that a crime has been committed is proven beyond a reasonable doubt. In an arson case, the testimony of the fire investigator as an expert witness is crucial in establishing the fact that arson has been committed. Defense counsel is certain to test the expert witness's credentials to try to persuade the court to rule against the investigator being accepted as an expert witness. The investigator should be prepared to establish expertise by documenting professional, life, and career experiences that contribute to expertise in fire investigations, as well as education and training. In such preparation, the investigator should maintain ongoing records of personal case investigations, education, and training. In preparing the case for court, the investigator must have a pretrial conference with the prosecutor to review the notes and evidence thoroughly. Courtroom demeanor and appearance must contribute to the aura of professionalism. The investigator must appear relaxed and confident in answering questions and avoid assuming a posture of defensiveness under questioning. All questions should be answered factually and without emotional displays. Nine footnotes are listed.