Psychology

Psychology is the science of the mind. An appreciation of what is happening of the mind of a criminal and why he or she acts as she does can be an important part of any investigation. A forensic psychologist (or psychiatrist, if they are medically qualified) can carry out a number of functions, such as assessing the mental stability of a suspect, building a psychological profile of the perpetrator and victim, and trying to understand the motivation for a crime.

Psychological tests can be useful in learning more about a suspect and their behavior. Standardized personality screening tests, of the kind that are sometimes also used in recruitment, can reveal the suspect's basic personality type. The tests are lists of questions to be checked which elicit responses about behavior, emotion, social skills, and beliefs. One common personality test includes the Minnesota Multiphasic Personality Inventory (MMPI), which can reveal if someone is suffering from a mental disorder such as anti-social personality disorder.

The psychologist may also use more subjective tests known as projective tests, which reveal more about inner conflict, fantasies, and thought processes. In the widely used Rorschach inkblot test, the suspect is shown a series of abstract inkblots and asked to describe what he sees. Another approach is to ask the subject to draw something like a house or a frightening scene. This can be very revealing of the suspect's fantasies and may be in complete contradiction to what they actually say to the psychologist.

The third kind of psychological test that may be administered is a cognitive test that measures the suspect's intelligence, mental competency, thought processes, and ability to understand his or her behavior. A common example is the Wechsler Adult Intelligence Scale. Less structured interviews will also be carried out, where the suspect may be encouraged to talk about their family, childhood, relationships, and problems. The psychologist will lead up to a discussion of the events that brought the suspect in for interrogation and try to find out how they feel about what happened. Of course, many suspects lie, but a skilled psychologist will be able to sort out the truth from the fiction by analysis of the subject's body language.