National Bureau of Investigation Private Investigation: The Serious Incident Every once in a while a private investigator will be interviewing a witness concerning a serious incident such as a wrongful death, aggravated assault or rape. The witness says or does something that causes the PI, who is most likely a criminal defense investigator, to believe the witness is not a witness at all, but the guilty party. The PI switches to the interrogation mode, but what is that mode? Interrogation experts say that an interrogation should consist of three stages: (1) establish rapport, (2) let the suspect tell the story and (3) challenge the story. In the rapport stage the interrogator engages the suspect in innocent conversation such as asking questions about the suspect's hobbies, interests and so forth. The objectives are to assess the suspect's intelligence and attitude; get the suspect use to talking; and establish a relationship in which the interrogator is the dominant person.