Criminal psychology is study of the criminal mind to understand why they commit crimes, but it can also be used when trying to profile criminals. By getting a psychological evaluation on the criminal before they are caught based on crime scenes or the nature of the crime, it can help law enforcement to know what to look for when apprehending their criminal. Criminal psychology is also an important factor in the legal system. It is used to evaluate the person's mental state during the crime they committed, but also at the present moment determining if they can stand trial. Overall, criminal psychology is a very helpful area of study, not only in the sense that it's the study on the criminal mind, but it's ability to also help to catch criminals quicker and more efficiently.
What is Criminal Psychology?
Criminal psychology is essentially the study of why people commit crimes, but it can also branch out to assessing criminals to determine their motive, and also by helping out in the legal system. Interviewing different criminals to understand their motives and get an idea of who they are is also a large aspect. One of the most well known tasks of a criminal psychologist, in particular, is offender profiling. This is a great tool utilized by the FBI when trying to track down criminals. The main goal of profiling is to provide law enforcement with a good portrayal of the criminal so that they can be apprehended. But it also is a necessity in the process of interviewing so that the investigator knows how to go about the interview. Knowing a criminal's mind can be a really great strategic method when trying to bring out a confession or understand the criminal better. 
Criminal Psychology's Role in the Legal System
Psychology, in particular, criminal psychology plays a major role in the legal system. The study of the criminal mind in any court case can help to evaluate the situation at hand, and can benefit both the authorities and the criminal involved. The purpose of criminal psychology is to get inside of the criminal's mind and understand their behavior. This is very useful when studying crime scenes during the investigation process. This way psychologists can know how the crime was committed, and what kind of criminal they are dealing with. This is helpful to understand why the crime occurred in the first place. 
Once convicted, a criminal must stand trial. Before doing this though, if the situation calls for it, they will receive a psychological evaluation. Not only does this determine their motive for committing the crime, but it also determines their sanity level. It can also be determined that the individual was insane during the offense, in which case the criminal can be charged with a less severe sentence or attend therapy. It is important to understand the individual's mental state during the offense. The cause could be insanity, voluntary alcohol or drug intake, or diminished capacity. Diminished capacity is the ability to understand what is going on, in other words was the individual aware of the actions they were making. If the the criminal standing trial is deemed to have some mental illness, then they are seen as unfit to stand trial. They can not, therefore, stand trial for themselves. Often in these cases, the individual will receive therapy in hope to rehabilitate them. In most cases of serial killers it is found they can not be rehabilitated, and if they are released, they will kill again. Depending on the severity of the crime, the criminal may be released as long as they try to rehabilitate themselves. But in other cases, the individual is sent to prison for many years. Others in extreme cases are put to death, depending on the legality of the death sentence in their area.
Profiling of Serial Killers
One main area that criminal psychology can be applied is during the profiling of serial killers. Obviously, it can also be applied to any area of profiling a criminal, but this section has a specific focus on serial killers. A serial killer can be defined as one offender who has killed two or more victims occurring on separate occasions. Profiling is used when trying to track down a killer by determining different aspects of the crime scenes, the common theme of victims, and any other common thread points. For example, the race of the victim is often the same race as the offender. The crime scene is also a good indication of the personality of the criminal. If the crime scene is extremely well planned out, then the killer is most likely intelligent. The condition of the victim can also show the mental state of the killer. These key clues are used when investigating who the killer may be. Although the profiles are not always completely accurate, they are usually close enough to the point that when the killer is finally caught, it is easy to tell right away that they were the one that committed the crime. 
One prime example of a well built criminal profile is that of Ted Bundy. All of his victims were Caucasian females who were thin and attractive. This showed that he was most likely a good looking male, very non-threatening and seemingly ordinary. As stated, killers most often go after victims that are the same race as them. There were many victims across the United States which also said that he had access to a vehicle. The way he lured in victims also showed that he had charm and was very persuasive. His crime scenes were always left in a very clean condition leaving no solid evidence that he was ever there. This shows he was very organized. The fact that all of his victims were woman, and that most crimes done to them before death were sexual shows that he had a dependency on women. He wanted to feel power over women, and killing them and taking advantage of them was his choice. Ted Bundy was caught, not on the pretense of an actual killing, but for a traffic violation. Using the profile they had they were able to determine that not only was he a traffic offender, but also a serial killer. The profile built of him was nearly perfect. 
This video is a great representation of what exactly criminal psychology is, told by a clinical and forensic psychologist.
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