Rape (forensics)

DEFINITION: Unlawful sexual intercourse with a person without that person’s consent.

SIGNIFICANCE: An inherently violent crime, rape is most often directed at women and children. The fact that rape is one of the most underreported crimes in the United States poses special problems for investigators as well as for attempts to prevent this crime and to collect data on its prevalence.

The crime of rape is one that generally involves offenders acting out issues of power and control over their victims. The sexual gratification experienced in normal sexual relations is generally a secondary motivation to those who commit rape. Most rape offenses fall into one of two mutually exclusive categories: cases in which victims already know their assailants and those in which victims do not.

According to the special report Female Victims of Sexual Violence, 1994–2010 (2013), data collected in the National Crime Victimization Survey, 1994–2010 conducted by the US Bureau of Justice Statistics showed that 78 percent of all victims of sexual violence (including both rape and sexual assault) are assaulted by people whom they already know. This is particularly true in cases of date rape, or acquaintance rape, which occur when offenders and their victims are together for social occasions. When rape victims are the spouses of their assailants, the assaults are termed marital rape or spousal rape. Assaults on persons under the legal age of consent are classified as statutory rape. The work of investigators in all these cases is made simpler by fact that victims can usually identify their attackers easily.

Serial and Stranger Rape

Serial rapists are predators who frequently stalk their victims and commit most of their offenses against strangers who are unlikely already to know them. Investigations of serial rape and other stranger rape cases thus have the added challenge of investigators’ need to find that identifies the offenders.

Serial rapists generally take great care to conceal their identities and disguise their appearance from their victims. This behavior increases the difficulty of identifying them. At the same time, however, each serial rapist tends to repeat predictable patterns of behavior—the offender’s so-called (MO), or method of operation. Offenders’ distinctive MOs, trademark behaviors, and psychological signatures all provide evidence that helps investigators to connect similar rape cases and eventually track down the offenders.

Psychological Evidence

Building psychological profiles of offenders is central to most investigations of serial and stranger rapes. The Federal Bureau of Investigation (FBI) has developed a system called criminal investigative analysis that examines the known behavior of unidentified offenders and builds psychological profiles that can be used to link offenders’ personality traits to physical evidence. The combination of criminal investigative analysis, physical evidence, and crime scene reconstruction provides the structure and direction for successful rape investigations. Most important, it provides a means for rape investigators, forensic profilers, and scientists to work collaboratively.

The FBI’s National Center for the Analysis of Violent Crime (NCAVC) has developed a system for classifying the core behaviors of rapists. Psychological profiles alone do not enable investigators to identify specific suspects, but suspect profiles can help investigators find matches in databases of signature behaviors, travel distances, victim profiles, and similar information. The goal of comparative case analysis is to identify rape offenders by matching their psychological core behaviors, methods of operation, and psychological signatures with information in the databases. Among the behavioral variables of rapists that are entered into database records are the following: methods of approaching victims, techniques used to control victims, amounts of force used, sexual dynamics of the rapes themselves, methods of evading detection, and postoffense behaviors.

Rapist Typologies

The NCAVC places rapists in four primary categories based on their behavior: power-reassurance, power-assertive, anger-retaliatory, and anger-excitation. Rapists in the power-reassurance category generally execute surprise attacks and initially reassure their victims that no harm will come to them. These rapists also tend to pay compliments to their victims and act almost apologetically for the harm they are inflicting. Sometimes, they ask their victims to evaluate their sexual performance in order to meet their need to be reassured. They tend to use minimal physical force to achieve their objectives.

Rapists classified in the power-assertive category assume immediate and strong command over their victims, to whom they give specific sexual instructions. Tending to use profane language throughout their rapes, their goal is to demean and humiliate without regard for their victims’ feelings, pain, or distress. Rapists in this category may carry weapons and generally use from moderate to excessive force in their attacks; they may apply brutal force to victims who resist.

Anger-retaliatory rapists initiate their sexual assaults with immediate applications of physical force and often use weapons of opportunity they find at the scenes. Their devastating blitz attacks combine with their angry and unsympathetic manner to overcome their victims rapidly. Male rapists in this category generally harbor deep-seated hatred of women. Their female victims serve as symbolic targets on whom they release their rage.

Anger-excitation rapists are sadists who often engage in violent, antisocial behavior to serve their obsessive and compulsive need to dominate others. In their initial approaches to their rape victims, they try to establish mutual trust. However, after they get their victims under control, the victims’ distressed responses to the physical and emotional pain they are experiencing stimulates these rapists sexually. Investigators of crimes committed by anger-excitation rapists must be alert to signs indicating that the rapists are becoming more violent and possibly are escalating into serial killers.

Another typology model published in 1990 by Knight and Prentky divides sex offenders into three categories: opportunistic, pervasively angry, and vindictive. Opportunistic rapists commit impulsive, unplanned sex crimes. They do not show signs of anger unless their victim resists. Like opportunistic rapists, pervasively angry rapists are also impulsive. Unlike opportunistic rapists, however, pervasively angry rapists are violent during their attacks, whether or not their victim resists, and may end up hurting or killing victims who resist. Vindictive rapists are not impulsive, but instead plan their attacks ahead of time. Such attacks involve humiliating and degrading the victim.

Physical Evidence

Rape investigations are multidimensional, interdisciplinary, and team-oriented. Successful prosecutions of rape cases draw on the professional expertise and training of both investigation teams and forensic specialists. Sexual assault response teams of law-enforcement agencies typically include four members: first responders, investigator/detectives, victim advocates, and sexual assault nurse examiners. All of these specialists play roles in the collection of the forensic evidence that is critical to establishing that rape crimes have occurred.

Most of the collected in rape investigations is found at the scenes of the crimes, on the bodies and clothing of the victims and the suspected offenders, and at so-called dump sites, where items connected with the crimes may have been discarded. Investigators look for trace evidence left on victims’ clothing; signs of physical injuries to the victims, including bite marks and bruises; and trace evidence left by the offenders, including blood specimens, hair, semen, fibers, soil, and bits of vegetation. To assist in organizing and protecting the evidence that is gathered, investigators use specially designed sexual assault evidence kits, which are commonly known as rape kits.

Medical examinations of rape victims are conducted by sexual assault nurse examiners and attending physicians. These teams make a special effort to gather biological evidence left on victims’ bodies by their assailants; when such material contains DNA (deoxyribonucleic acid), analyses can result in DNA profiles that can be fed into the database of the Combined DNA Index System, better known simply as CODIS. Administered by the FBI, CODIS contains DNA profiles collected from throughout the United States, from samples taken from both convicted offenders and unsolved cases. If a match is found with a potential suspect, this gives law enforcement probable cause to collect a known DNA sample from the individual. An unfortunate limitation to this system, according to the National Institute of Justice, is that the evidence contained in hundreds of thousands of rape kits has never been processed, so the potential resulting DNA profiles have not been sent to CODIS; hence a wealth of potentially valuable information on rapists is not available for comparison.

When rape victims are examined, large pieces of clean butcher paper are placed under them while they disrobe to reduce the chances of losing potentially valuable trace evidence that falls from their bodies and clothes. After the victims disrobe, their clothing is carefully examined for trace evidence. Each individual piece of clothing is packaged separately; moisture stains are dried out, and sheets of paper are inserted between folds of clothing for additional protection against cross-contamination.

When bite marks and other injuries are found on the bodies of rape victims during their examinations, photographs are carefully taken of the wounds as soon after the attacks as possible. Additional photographs taken about forty-eight hours later often prove valuable in documenting emerging bruise marks. Photographic evidence is often presented to juries in rape trials to demonstrate the extent of physical injuries inflicted during assaults.

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