An interview is usually conducted for the purpose of gathering information from people who have or may have the knowledge needed in an investigation. The interview has three major requirements, that are: the presence of the interviewed, consciousness, attentiveness to what is happening. It is non-accusatory and has a system of question and answer. During the interview there should be a 20/80 system, the investigator should take 20% and the person being interviewed 80%.
Interrogations are different than interviews because interrogations have four major objectives that are: eliminate the innocent, obtain valuable facts, identify the guilty one or obtain a confession. In this case, the examiner believes the person that is being interrogated is either guilty or has lied during an interview. Because of this logic and rational arguments based on pieces of evidence are used. The interrogation uses the monologue system which the examiner makes statements that are used to persuade the subject of the interrogation.
The main difference between an interview and an interrogation is that interrogations have to follow a tight row of legal requirements by the Constitution or other laws. Interviews are usually less formal and are conducted in a cordial atmosphere while the interrogations are usually held in an uncomfortable atmosphere - usually an interrogation room - and the one who conducts the interrogation uses psychological pressure.