Friends of the Forensic Science Club, this week we present the paper “Predicting rapist type based on crime-scene violence, interpersonal involvement, and criminal sophistication in U.S. stranger rape cases”, by Mellink, I. S. K.; Jeglic, E. L. and Bogaard, G. (2022), in which authors carry out a study in which they investigate the particularities of serial rapists and single-victim rapists cases, to know which are the proper elements of each case and make a comparative analysis that helps in the criminal profile of similar cases. 

Sexual violence is a serious public health problem worldwide. Only in the United States, one in six women has been the victim of attempted or completed rape in her lifetime. Therefore, there appears to be an urgent need to better understand those who commit sexual assault in order to increase conviction rates. 

Physical evidence, such as DNA or fingerprints found at the crime scene, is often not found or, if found, may not be conclusive. Therefore, if we establish a link between the crime and the offender using other means, it will be valuable to the investigation by narrowing the list of potential suspects. 

Criminal profiling is one of many techniques that aid in the process of investigating, identifying, locating and arresting offenders in general and in rape cases in particular. 

In criminal profiling, crime scene characteristics are used to infer information to help narrow down the suspect list and apprehend the offender.

By attending to observable crime scene behaviors, police forces can identify clues about the type of offender they are dealing with, such as the likelihood that the offender is either a serial rapist or a single-victim rapist. 

Why is this last point important? Precisely because, if there are crime scene characteristics that associate the case with the offender being a serial rapist, this could indicate that he has committed other similar crimes, which, in turn, would give investigators the idea to search their databases for the criminal history of suspects and, thus, reduce the list of possible offenders. 

To better understand those who commit violations, offenders can be classified based on behavioral or modus operandi variables.

From the point of view of most experts, rape is viewed as an event in which the offender treats his victim similarly to how he would treat others in a non-criminal context. 

This, coupled with other findings, suggests that it is possible to link a crime and an offender by their behavior. This linkage is based on two ideas: consistency and variability. Consistency refers to the fact that a subject’s criminal behavior is consistent, meaning that the same person is likely to behave similarly in other crimes. And variability is based on the fact that two offenders will not behave in exactly the same way, which makes it possible to distinguish between them. 

Authors decide to focus on the differences that exist between serial rapists and single-victim rapists and that can be extracted based on their behavior at the crime scene. There is a dearth of empirical literature on this, but a 1987 study gives some interesting insights, such as that single-victim rapists are more likely to be known to their victims than serial rapists, and prefer to use a safe approach rather than a quick attack. With serial rapists the opposite would happen. 

In the present study, authors used data relating to the cases of 3,168 inmates in a New Jersey prison, who were serving time at the time of writing for sexual offenses. 

They found that single-victim rapists and serial rapists can, indeed, be differentiated from each other based on their behavior; and further, experts often classify the cases according to three categories: violence, criminal sophistication, and interpersonal behavior. 

Single-victim rapists are more likely to have a crime scene with violent characteristics, and are more likely to digitally penetrate and threaten their victims. 

Serial rapists, on the other hand, have a more criminally sophisticated crime scene, for instance, they incapacitate the victim or use a weapon. This is in line with previous research showing that serial rapists are more sophisticated in general. 

Serial rapists are more likely to use weapons, which tends to be a gun or knife, and, in addition to incapacitating their victim more often, as mentioned above, they also tend to groom the victim and guide or lure them somewhere. These types of rapists are also less likely to use drugs or alcohol during or immediately prior to the crime in order to remain criminally sophisticated and avoid detection, as it does not pay for them to risk their success by using these substances. 

Despite gaining some interesting insights, authors point out the need for further research on the entire criminological process of rape, from victim to perpetrator, and what is related to the crime scene, as only by knowing and understanding these data will we be able to improve prevention.

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