Linkage analysis is one component of profiling, a method that is part science and part art and is used to analyze a crime and to develop a profile of the type of person who might commit such a crime. In linkage analysis, investigators study two or more crimes, looking for similarities. They are trying to determine whether the crimes might have been committed by the same person. They look to see whether the method of operation, or MO, was the same or different, and whether either or both crimes involved any ritualistic behaviors that could be used to characterize the suspect.
The MO includes those acts necessary to accomplish the crime and the consequences of those acts. For example, shooting a victim with a gun, with the consequence being that the victim dies. In contrast, a ritual is an act unnecessary to the commission of the crime that is carried out in order to meet the emotional needs of the offender. Common examples of ritualistic acts include excessive brutality (in particular, damage to certain parts of the body), biting (typically an anger-motivated behavior that may be done randomly or target particular sites on the body), injurious anal penetration (also an expression of anger), manual rather than ligature strangulation (use of the hands makes the act more personal), and injuries inflicted from the front, so that the offender can see the victim's face and watch their anguish. With these behaviors or rituals, the offender is expressing his perverse pleasure in harming the victim.
Ritualistic behaviors can fall into several categories: cultural rituals, religious rituals, psychological rituals, and psychosexual rituals. Psychosexual rituals, which represent the mental and emotional component of the human sex drive, are sometimes evident in crimes involving excessive brutality and sexual assault and mutilation. The individual who engages in psychosexual ritualistic behavior is attempting to gratify the psychosexual drive.
There are two general categories of sex offenders: impulsive offenders, who seldom have ritualistic behaviors; and ritualistic offenders, who almost always have rituals associated with the commission of a crime. Furthermore, these categories are not mutually exclusive; some offenders will be impulsive and perform ritualistic acts.
Crimes can be linked by a single ritualistic behavior or by a unique combination, or pattern of behaviors, called a signature. With this unique pattern of ritualistic behaviors, the offender leaves his or her "signature" on the crime. In the case of linkage between two signature crimes, it is not just the similarities between the two incidents that are important, but also the uniqueness of the combination of behaviors.
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