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Evidence Collection in Sexual Assault Cases

Roughly every 73 seconds, someone is sexually assaulted in the United States. While some of these victims may choose not to disclose their assault, those that report typically undergo a forensic examination, during which they are assessed for injuries and any evidence that could be used to identify the perpetrator. 

In the aftermath of a sexual assault, evidence collection is an important procedure. Certain types of evidence can confirm sexual contact, reveal whether force or coercion were used, and help officials identify a suspect through DNA analysis.

Today, evidence collection is the most common way of substantiating that an act of sexual violence occurred, according to the authors of STM Learning’s Medical Response to Adult Sexual Assault, Second Edition. While evidence collection can be an extensive process, the forensic examiner’s work is vital in understanding what happened to the victim and bringing the perpetrator to justice.


DNA Collection

Oral, anal, vaginal, and skin swabs are the most common samples taken for DNA analysis following a sexual assault. Samples of hair, blood, skin, cells, saliva and sweat can also be collected from the victim. 

If the victim recalls skin-to-skin contact from the assailant (eg, exerted pressure from being held down, oral contact), wet swabs should be taken from the reported area. In the event that the victim reports scratching the assailant, swabs can also be taken from under the victim’s fingernails.

Discovery of acid-phosphatase, a chemical found in semen, has been found to be substantial in DNA identification. A lack of semen or seminal fluid does not necessarily mean that sexual contact did not occur.

Blood and Urine Collection

If drugs have been used to impair the victim of the assault—a situation known as drug-facilitated sexual assault—blood and urine samples should be collected for a drug screen analysis. While knowing the substance the assailant used can be helpful in terms of evidence collection, understanding what toxins may still be present in the victim’s body is just as important for their health and treatment. 

Although these collections are time-sensitive, technology has improved over the years to allow a longer window of time for drug-related evidence to be collected.

Debris and Clothing Collection

Debris, including fibers, leaves, dirt, sand, and gravel, can help investigators in identifying the scene where the sexual assault took place. These types of materials are often found on the victim’s body, clothing or shoes.

These findings can be especially important if the assault took place somewhere the victim otherwise would not be or does not visit frequently. When collecting debris, it is best to do so using a sheet of paper or paper towel. The paper should then be folded to safely store the debris inside. 

Any clothing worn by the victim during the assault is examined, and items that could be evidence are collected. Particular attention should be given to examining the pieces of clothing that have been torn or stained. The material could hold the assailant’s DNA and help corroborate their use of violence.

Injury Assessment

During the examination, the forensic nurse will assess any injuries obtained during the sexual assault, including nongenital injuries and anogenital trauma. Although nongenital injuries are rare, it is the best proof of force used during an assault. 

Anogenital trauma can also help determine if force was used during the assault. Devices such as colposcopes and anoscopes have allowed injuries that are not always easily seen to be more clearly identified.

Photo-documentation

Photography has become a common method for forensic examiners to document injuries sustained by patients during a sexual assault. Images can assist examiners in identifying injuries and may also be used as demonstrative evidence during court proceedings.

With the patient’s consent, the forensic nurse will document the genitalia in detail. Full-body shots are also recommended, followed by mid-distance and close-up photos of any areas of interest. In some cases, such as when nonfatal strangulation is reported, taking more detailed photographs of the neck, head, eyes, and other areas can be useful as well.


For a full explanation of the evidence collection process for sexual assault patients, please visit the National Center for Biotechnology Information’s website.

This blog was written by STM Learning’s editorial staff for educational purposes only. It is not intended to give specific medical or legal advice. For expert information on the discussed subjects, please refer to STM Learning’s publications

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