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Explain how a Forensic Psychologist prepares the profile of a serial killer.

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Forensic psychologists contrast with forensic scientists, who collect and study physical evidence associated with a crime. Forensic psychologists are interest, as the name suggests, in the mental profiles of perpetrators and victims of crimes. Understanding many crimes, especially violent crimes involving murder and/or rape, is essential to forensic psychologists for developing profiles of the types of individuals most likely to engage in such crimes.

It can be difficult to ascertain the reasons why an individual has engaged in violent criminal activity, even when that individual is in custody and subject to interrogation. Developing profiles of unknown violent criminals, whose identities are not yet determined, is even harder and another matter altogether. That is why forensic psychologists study histories of known criminals from the past and present. In order to understand why a particular crime or series of crimes is occurring or has occurred, it is essential to develop a profile framework for the specific personality and physical traits of individuals known to have committed a given type of criminal activity.

In a case of homicide, a forensic psychologist, as with other investigators associated with the case, will carefully study the physical evidence for any particular sign or mark of a quirk or signature that may indicate a personality trait or that a specific type of personality was behind the crime. For example, does the perpetrator have a pattern of carving something into the skin of the victims, or does he or she (usually a he) intentionally or inadvertently leave behind some form of DNA evidence such as saliva (e.g., does he bite his victims in the course of the rape and/or murder)? Does the perpetrator leave behind notes intended to explain his actions or to taunt the police officers he knows will be seeking to identify and capture him. It is the responsibility of the forensic psychologist to study this evidence and, drawing from experience and knowledge of past cases and criminals, develop a profile of the specific perpetrator that can help to narrow down a field of suspects and eventually identify the correct individual.

For example, if a forensic psychologist is able to determine that the perpetrator acted violently in a calm state, as opposed to an agitated, possibly irrational state, then the investigative team knows that it may be dealing with a seriously psychotic individual who feels no remorse whatsoever over his actions, or they (the investigators) may be dealing with a professional who knows how to cover his tracks in a more methodical way than would be the case for an agitated criminal who, acting more impulsively, leaves behind more physical evidence of his crime, such as fingerprints, hair, bodily fluids, etc.

Forensic psychologists are also important to the process by which captured suspects are interrogated and studied for potential signs of guilt. By observing the interrogation of the suspect, the psychologist, again applying knowledge and insights gleaned from previous experiences and studies, is able to help other investigators determine with a higher level of accuracy whether the suspect in custody is fabricating statements or is, in fact, telling the truth. It is not just the words emanating from the mouth of the suspect, but his or her visual "signatures" that helps forensic psychologist interrogator determine the nature of the individual with whom he or she is interacting. Whether the suspect is calm and deliberative, or appears agitated, nervous, ill-at-ease, is important in determining the suspect's state of mind. Does he or she appear delusional, or is he or she merely lying to avoid further suspicion? All of this is instrumental in narrowing a field of suspects and identifying the one guilty party.

At the end of evidence analysis and psychological analysis, the forensic psychologist puts together a report identifying the salient characteristics of the criminal being sought. Those characteristics include gender, employment, motivation (such as revenge), psychological pathology (such as post trauma stress syndrome or paranoia), age, personal traits (such as habits, cleanliness, clothing), nationality, educational experience, marital status, living arrangements (such as living alone, living with strangers who are roommates, living with relatives), parental status (such as divorced, dead, still living). The forensic psychologist puts the elements all together and (from the psychological, physical, social, personal picture presented) makes a prediction of what might be expected to be true when the person is arrested, such as they might be at a cinema, might be drunk and disorderly, might be impeccably dressed. Psychologist James A. Brussel made the first criminal psychological profile, profiling a serial bomber, in the 1940s, establishing the model for psychological profiles and correctly predicting that the bomber would be "wearing a buttoned up double breasted jacket" when arrested.

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