Sexual Assault Investigation

Published 16 Feb 2017

Sexual assault is one of the most under reported crimes. Both men and women can become victims of sexual assault, although all related statistics are associated with women. Sexual assault is a broad classification for all unaccepted sexual advances or exhibition of sexual desires. It differs from rape which is the gratification of sexual desire by force. The National Crime Victimization Survey data suggests about half a million people had been sexually assaulted between the years 1992-93. More recent surveys like that for 2001, estimates there were around 249,000 sexual assault victims for that year (Online Lawyer, 2008). However these figures are presumed to be too less due to the underreporting factor. A 1992 study suggests that only about 16% of the sexual assaults are brought to the police.

The main reason for victims to shy away from reporting these cases is perhaps to avoid the embarrassment of being talked about it in the neighborhood, the media or at least being asked to narrate the happenings before a jury. Although sexual assault is an underreported crime it is however possible for anyone to falsely raise charges of sexual assault, even without any evidence. A charge of sexual assault on someone can be very damaging and can even devastate one’s life. Thus sexual assault investigations are very crucial, particularly when the suspect denies charges; and physical evidences are very important in the investigations. The evidences collected against the offender are of varying nature like material evidence, biological evidence, medical evidence etc. and requires the expertise of physicians, laboratory technicians and crime scene investigators to compile them.

It has been overwhelmingly observed that most sexual assaults and rapes are committed by people well known to the victim. This aspect of rape has considerable bearing on the investigation and prosecution of the perpetrators (Kilpatrick, 2000). As the identity of the perpetrators are known to the victims in most cases, the investigation here need not be focused on the identification of the suspect or perpetrators. In most cases, the perpetrator would proclaim that the act wasn’t a rape, but only a consensual sex. Therefore the investigation should be more directed to counter this position. Known offenders adopt such a stand as it is difficult for them to plead a case of mistaken identity. To prove a sexual act as a case of rape and not a consensual decision, the victim needs to show proof of physical injuries (Estrich, 1987). As most rape victims actually don’t receive major physical injuries, the investigators and prosecutors face a difficult task, as absence of injuries is generally perceived as consenting. Forensic examination may highlight physical injuries that are relevant to forced rape, which may then be used as evidence.

The crime investigating officer, at the location of the sexual assault or rape, needs to primarily look to the requirements of the victim, like medical help. The officer needs to interact with the victim and try to boost her morale and confidence, particularly when the victim is in a state of shock or even hysteric. At the initial stage of the rape investigation, the investigator should look for any physical material of the attacker present with the victim. Generally a rape victim would tear the clothes of her attacker, scratch and scar his face or even pull his hair. Thus there is always a chance of the assailant’s hair, clothes or blood stains on the victim, particularly on her hands and under the nails. It is important to have the clothing of the victim sent for analysis, at the earliest possible, but care should be taken here to ensure that the victim is comfortable and not pained by further embarrassment. The evidence material must be gathered, handled and packed carefully before it is sent to the lab for forensic analysis. The number of people handling the evidence should be minimum and the investigator needs to fix his initials to the evidence for its accuracy. Semen and hair are very valuable physical evidences.

A medical examination is part of the rape investigation and should be carried out by a specialist in forensic medicine. The victim would mostly insist on a personal physician performing the exam, which should be strongly discouraged; as personal and private physicians would not have rape investigation experience, or be able to testify in a court to get a conviction. The medical examination would include visual examination of vagina and determination of tissue damage (ASU, 2006). The presence or absence of a rapists’ sperm is concluded by carrying out a pap smear test. When rape results in the death of the victim, then the examination should also include anus, mouth etc.

A forensic medical examination considers a victim’s body, as a crime scene. Based on the victim’s version of the incidents, the forensic team collects evidence which can prove, the identity of the perpetrator, and that rape had occurred. When the suspect denies any sexual act with the victim, then DNA or other appropriate material evidence is collected which can prove that the suspect had committed the sexual act. Claims of consensual sex cannot be countered easily and proof of physical injuries is one of the few ways to counter such claims. Newer technology enhances detection of physical injuries, like the use of colposcope. The colposcope is generally used by gynecologists for observation of vulvar or vaginal diseases. The colposcope provides a 30 time magnification of areas like anus, vulva or vagina. Injuries like abrasions and tears that are not visible to the naked eye are observed with the colposcope. Earlier rape examinations without colposcope could establish evidence of genital injuries in about 19 to 28% of cases. Now with the colposcope about 87% of genital trauma can be established.

Crime scene processing involves examining, identifying, recording and collection of physical evidence based on which comparisons, recognition and individualization are later made. Considerable care should be given when evidences are collected and preserved. As plastic enclosures cause moisture formation, all evidence items should be air dried in a room, before packing. This can prevent fungal and bacterial growth. Dry items which are possible biological evidences need to be wrapped first in a clean paper, then put in a paper bag. When biological stains are formed in materials like cloths or rubber, and the items need to be folded prior to packing, then care should be taken to ensure that the specimen area is not folded. Otherwise, the biological material may be damaged and DNA testing would become difficult (Savino, Turvey and Baeza). Solid objects bearing biological material evidence, must have clean paper covering it and sealing the stained area, to prevent contamination or dilution of evidence.

Victims of a sexual assault need to be brought to a medical facility within 72 hours of incident, where a SANE (Sexual Assault Nurse Examiner) conducts the medical examination. In case the victim is brought after 72 hours, it would help if the victim has not changed clothes or has not showered. It has been established that the best evidence of assault could be gathered when the victim reports within 12 hours of the incident. The evidence collection procedure of the SANE has evolved over the years as a consequence of interactions with investigators, crime lab specialists and attorneys. Today, the collection of evidence is more complete and valid and contributes immensely in charging a suspect. The forensic examiner also collects blood and saliva samples of the victim to differentiate it from that of the perpetrator. Sometimes an extra blood sample of victim may be required for alcohol or drug analysis. This is required when perpetrators claim victims to have agreed under the influence of alcohol or had agreed to have sex in exchange of drugs. When sperm or seminal fluid of the offender is not seen in the victim, then too rape shouldn’t be ruled as studies have shown that a good percentage of rapists are sexually dysfunctional or use condoms. Nowadays seminal fluid evidence is more used in determining DNA evidence linking to the suspect. Seminal fluid can also be investigated for prostatic specific acid phosphatase (PAP 30) which are highly concentrated in seminal fluids compared to vaginal fluids.

Genital trauma evidence can not only support the victim’s version of the incident, but also prove that force was indeed used. The position of the genital trauma is related to the body position of the victim during the assault. For instance, when there is injury to external vaginal opening, the woman is most likely to have been raped in missionary position. When a semi-circular cut or scratch is observed in the inner vaginal wall, then a digital penetration is supported (Ledray, 1999). The colposcope plays a vital role in genital trauma examination. Although genital trauma indicates use of force, absence of genital trauma should not be considered as consensual sex.

Physical evidence collected in rape cases are directed towards establishing occurrence of penetration, establishing occurrence of nonconsensual sex and establishing identity of the perpetrator. The absence of seminal fluid may also be attributed to several causes like suspect not ejaculating in the vagina, or the medical examination was done after a long time after rape, or the doctor having failed to take a proper sample. Occasionally seminal fluid from a consensual sex would be present, while that from a rape would be absent. In such cases seminal fluid typing would be carried out. Evidences like torn or soiled clothing, bruises, cuts, plucked hair indicate fight or struggle during intercourse, and hence rape (Fischer, 2003). Finger prints, palm prints and even foot prints are valuable clues that help to nail the assailant. Fingerprints from beer cans, cigarettes etc. are required to identify the assailant. For drug aided sexual assault, blood and urine samples are crucial evidences. Victims who suspect the use of drugs, should not empty their bladders. Substances like GHB (gamma hydroxybutrate) which can easily make a victim unconscious, is eliminated from the blood within six hours but would be detectable in urine after that. When any pills or suspicious powder are found at the rape scene, the investigator should not ignore these.

Although physical evidence collection and forensic analysis can help in identifying the assailant, investigators need to be aware of the circumstances and situations to profile the assaulter. As sexual assault are committed on people of both sexes, children, adults and elders; investigators should look for appropriate physical evidences. Similarly experience and expertise is required to identify a serial rape case based on evidence similarity and additional evidence recognition. In child molestation cases, physical evidence are much lesser, and signs like nightmares, bedwetting and urinary infections are considered symptoms of child molestation. Investigators can only look for clues on the child’s dress worn during the last assault, if it has not been washed. Beyond this, the investigators are totally dependent on medical observations. Child abuse is identified based on the observations of the pediatrician (Fischer, 2003). Strange bruises, broken bones as revealed by X-rays are important to the investigation. Sometimes unhygienic conditions and under nourishment may also be associated. For homosexual assaults, a SANE examines the rectum and takes a swab sample for presence of semen. Here medical examination can not only reveal whether sodomy had occurred, but also confirm if the victim was accustomed to it. Presence of lubricant or feces traces also need to be looked on clothing.

To make investigation and prosecution of rape cases more effective, the collective effort and cooperation of several agencies are required. The agencies involved in the investigation and prosecution of sexual assault include the medical personnel, law enforcement personnel, prosecution, correction and victim recovery services. The services are interrelated and a reporting at any point would get all the agencies into action.


  • Augusta State University, Department of Public Safety, Investigating and processing a sexual assault rape call: Initial Steps. (2006) [Electronic Version].
  • Online Lawyer Source. (2008) Sexual assault victims [Electronic Version]
  • Kilpatrick D.G., National Violence Against Women Prevention Research Center. Rape and sexual Assault (2000) [Electronic Version]. Downloaded on 2nd June 2008 from
  • Fischer B.A., Techniques of Crime Scene Investigation CRC Press. (2003)
  • Ledray. L., Sexual Assault Nurse Examiner (SANE). Development and Operation Guide, U.S department of Justice, Office of Victims of Crime. (1999)
  • Estrich, S., Real rape. Cambridge, MA: Harvard University Press (1987)
  • Savino J.O., Turvey B.E., and Baeza J.J., Rape Investigation Handbook Academic Press (2004)
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