DNA Forensic Testing and Use of DNA Rape Kits in Cases of Rape and Sexual Assault

Rape is defined as forcible penetration, whether oral, anal or vaginal using a sexual organ or object without consent of the victim. Mutilation of sex organs (infibulation, for example) or ritual abuse may also be considered rape. Sexual assault, on the other hand, refers to any unwanted sexual contact, including fondling and molestation; in actuality, it includes a broad spectrum of various types of sexual molestation. Both rape and assault do not necessarily need to be forced. Rape and cases of sexual assault vary from country to country. Accurate statistics are hard to come by as many cases of rape go unreported due to a number of reasons, including black mail, social stigma, shame and fear. Unsurprisingly, the American Medical Association states that rape is the most under reported crime. Semen detection tests, confirmatory tests and forensic DNA testing are indispensable tools for solving a cases of rape and assault in order to bring perpetrators to justice.

What is semen and how is it detected?

In many cases of sexual assault traces of semen are left behind on the victim’s body, clothes and the area/location in which the assault has taken place. Swab samples may be collected from areas of the victim’s body where the assailant is believed to have come into contact. Finger nail clippings may also be collected as these may contain traces of foreign DNA — from semen, skin or fecal matter. In such cases, collecting the perpetrator’s DNA as early as possible is crucial to increase chances of identification of the person who committed the assault.

Semen is composed of four main elements which are secreted from different glands, among these the seminal vesicle. Semen contains chemicals also secreted by the prostate, the epididymis and bulbourethral glands. Due to the fact that the morphology and size of human semen is unique, several tests which can be used to confirm its presence.

Semen can be detected in three ways using confirmatory tests. To keep in mind that semen confirmatory tests are not the same as DNA tests using sperm. A DNA test will not set out to confirm whether the biological sample provided contains semen but rather it’s attempt to extract a DNA profile of the individual to whom the sample belongs using the semen sample provided. Many companies such as The Genetic Testing Laboratories are able to extract a DNA profile from a semen sample so as long as this has been collected correctly and has not been contaminated.

The acid phosphate test is among the most common and is even available via home testing kits, which can be purchased online. The acid phosphate test detects a protein in semen known as acid phosphatise. The test is referred to as a presumptive test because these tests make use of a certain chemical to establish the presence of a certain body fluid or chemical. In forensic science, presumptive tests can do two things: they either exclude a substance from being semen or confirm with a good probability that the substance is semen. The acid phosphate test hydrolyzes the protein in the semen sample; consequently, if semen is actually present, a color change will be noted in the intensely colored azo dyestuff. Presumptive tests have the chance of false positive results, which can indeed be misleading. Further confirmatory testing is required following the results of a presumptive test that gives a positive result.

The Christmas tree test uses chemical reagents that color the head and tail portions of the sperm cells in different colors. This type of histological staining produces bright colors and is, thus, often referred to as the Christmas tree test. The test uses a dye called nuclear red solution, also called Kernechtrot dye — the term “nuclear” refers to the fact that the dye acts on the nuclear material causing the characteristic color change. The heads of the sperm will appear red and the tails will appear green following application of the Christmas tree test. However, the test does have its limitations as sperm cells tend to degrade very quickly following ejaculation. The chances of successful confirmation of sperm depends on how long after the assault a sample is analyzed. Due to the fact that the Christmas tree test dyes the actual sperm cells, the test will produce no results in males with aspermia.

The Rapid Stain Identification (RSID®) is a confirmatory test. It is done by means of a kit that contains an extraction/running buffer, water for swab wetting, swabs, scissors, transfer pipettes, tube rack, protocols, and RSID™-Semen strip tests. This test uses antibodies that are specific for specific for human semenogelin on an immunochromatographic strip to confirm the presence of a component of seminal fluid, Semenogelin. It should be carried out whenever a presumptive test gives a positive result.  The RSID test is very accurate and specific for human semen testing and will even prove effective in diluted samples of semen, semen mixed with other body fluids or the presence of fungi or bacteria — in other words, the semen test will not cross react. This is indeed an advantage as in cases of assault, cross reactivity between similar proteins (body fluids containing similar components) occurs frequently, and avoiding contamination between body fluids that may lead to inaccurate/ false positive or false negative results could pose problems.

DNA testing in order to extract a profile

Semen confirmatory tests will not help identify the perpetrator. In order to do this, investigators need a DNA profile. A DNA profile is essentially a set of numbers which will highlight the polymorphic regions on a person’s DNA; these regions are unique to the individual and a complete DNA profile can help accurately discriminate between different people. No two individuals can have the same exact DNA profile (with the exception of monozygotic twins). Once the DNA profile has been extracted it can be compared to the DNA profiles of any suspects to look for a match. In cases where no match is found, investigators and police might run a search in a DNA database. A DNA database will contain the DNA profiles of convicted criminals (the criteria for adding a person’s DNA profile into a government DNA database vary from country to country; moreover, there may be a time frame after which a DNA profile will be removed from the database). The USA has CODIS (the Combined DNA Index System), compiled and run by the FBI, as well as the National DNA Index System (NDIS). If a DNA profile extracted from a sample at rape scene is matched with a DNA profile in CODIS or NDIS, the identity of the suspected perpetrator may be known. However, a match between two DNA profiles does not necessarily confirm the person is guilty of the crime and is the true perpetrator. Other evidence will be needed to support the case.

Preserving evidence

Following rape or assault, the victim’s first instinctual reaction is to shower or wash — metaphorically, physically and psychologically cleansing themselves of the abuse suffered but in the process, also washing away any DNA evidence. Victims should refrain from changing clothes, washing, drying or brushing their hair; move, discard or touch any object the offender may have handled or clean the area in which the incident took place. At this point the preservation of DNA evidence is pivotal and washing away the evidence could hinder investigations, making it very difficult to have any tangible evidence an assault did take place. It is not uncommon for victims to feel uncertain about whether to report the crime — if they choose not to do so they should immediately opt for a medical forensic examination in a hospital (usually carried out by a sexual assault nurse examiner (SANE) or sexual assault forensic examiner (SAFE) who can store DNA evidence appropriately). The forensic medical examination can be quite taxing for the victim as it can take several hours to complete. The victim does, however, have a right to refuse any aspect of the examination  they are not comfortable with. A full examination of the body is recommended and samples of hair, urine, vaginal swabs or blood  may be taken. Any injuries sustained as a result of the assault will also be documented, described and photographed. Medical measures to prevent disease, known as post-exposure prophylaxis (PEP), may also be taken. Post-exposure prophylaxis may stop a virus from becoming established in the body of a person who has recently been exposed and enable the body to provide protection against the virus. One of the main diseases for concern in cases of rape or sexual assault is HIV. Antiretroviral drug treatment is used in such cases.

DNA Rape Test Kit explained

A DNA rape kit enables collection of biological material in cases of rape or sexual assault and may be used in cases of rape or sexual assault. A kit can also be referred to as a sexual offense evidence collection (SOEC) kit or Physical Evidence Recovery Kit (PERK). The kit is normally used by forensic experts to collect samples from the body of the victim. Inside the kit, one finds slides, swabs, white sheets, plastic bags and other items which can be used to store, analyze or preserve samples of semen, body fluids or hairs. The kits used are the essential tools provided to the victim and are used to collect whatever forensic biological evidence that may have been left. The evidence is most often semen collected either directly from the body of the victim — from the body itself or from non-living items such as undergarments or sheets. In a given situation, the material can be collected and analyzed by a forensic technician and then sent for examination in a laboratory. In an ideal case, the forensic samples collected, meaning the semen, saliva, skin or other biological material, are provided to a laboratory, which can then administer a full DNA analysis. The results in some cases can be used by law enforcement officers or a legal entity to bring the assailant to justice or provide cause for arrest.

Proving a sexual assault with DNA

While the forensic testing of genetic material can resolve many legal situations, it is not always a simple task. The tests performed by laboratories on DNA are only available to identify a person or persons who have provided their samples for analysis. There is currently no central database that contains all human beings’ genetic information. The reality is that technology can provide a match only: meaning if there is a forensic sample and there is a separate test performed on a suspect, the analysis can only tell if the two are a match or not. 

Recently, new options have surfaced to assist in identifying an unknown assailant. However, it’s a small sample when compared to the population at large. In many places around the world — in the United States for instance — a person charged or convicted with a crime (depending on the state in question) will be forced to submit their DNA to a criminal database. When a law enforcement agency is investigating a given sexual assault it is possible that they can compare their forensic samples to the database in hopes of finding a match. In other cases once there is a suspect found or identified, testing of this person can be required in order to prove or disprove their involvement in the crime. This technology is relatively new and laws protecting citizens from agencies looking at database DNA are constantly evolving.

For how long can DNA forensic evidence be kept?

DNA is relatively stable. It is most likely that forensic samples collected from a rape victim will yield results: however, time factors, chemical factors (such as washing using soaps and detergents), external factors (such as temperature and humidity) and internal factors (other bodily fluids) may affect the validity of a sample. The earlier samples are collected and tested the higher the chances of yielding solid, reliable results. The following are just some guidelines as to how long different DNA samples may remain viable:

• DNA from fingers in vagina — up to 12 hours.
• DNA from a penis — most likely to obtain a profile from the victim within the first 12 hours.
• DNA from skin to skin contact (e.g., on bruises, or from kissing) can be detected up to two days. This includes detection of body fluids, cellular material and lubricant. If by chance, the person has not bathed or showered then the Forensic Science service says that the relevant area can be swabbed up to 7 days after the incident.
• Fingernail scrapings — two days.
• Oral (saliva and mouth swabs) — two days.
• Lubricant from a condom — up to 30 hours.
• Anal — up to three days.
• Vaginal — up to seven days.
• Fibers of anything put on the head can last up to seven days.
• Semen can be detected on clothing despite washing.

In some cases of assault, the assailant may not have ejaculated, meaning no semen will be present on the victim’s body, and genetic evidence from semen cannot, thus, be extracted. In such cases all semen tests will fail. Alternative genetic evidence linking the perpetrator to the victim could be collected, including saliva samples from places where the assailant has licked the victim or cells from the perpetrator's penis that have been left behind in the victim's vagina.

Bibliography

Cooper, P., Spruce, C., Webb, L. and Borowitzka, A. (2014). Identification of Human Semen. A comparison of the ABA card, P30 and Rapid Stain Identification (RSID)- Semen Test Kits. 1st ed. [ebook] 1Forensic Biology Laboratory, PathWest Laboratory Medicine WA. Available at: http://www.seidden.com/Semen_archivo_1.pdf [Accessed 05 Dec. 2014].

Killick, S., Leary, C., Trussell, J. and Guthrie, K. (2011). Sperm content of pre-ejaculatory fluid. Hum Fertil (Camb), 14(1), pp.48-52.

Lifecentre.uk.com, (2014). Forensic evidence collection in sexual assault & rape. [online] Available at: http://www.lifecentre.uk.com/police_info/gathering_forensic_evidence.html [Accessed 12 Dec. 2014].

National Institute of Justice, (2014). Extending the Time to Collect DNA in Sexual Assault Cases | National Institute of Justice. [online] Available at: http://www.nij.gov/journals/267/Pages/extending.aspx [Accessed 16 Dec. 2014].

Ncdoj.gov, (2014). [online] Available at: http://www.ncdoj.gov/getdoc/0c6b24c3-af68-4efa-a0e7-17a55f1b1147/Body-Fluid-SOPs-Rev-O6.aspx [Accessed 09 Dec. 2014].

Nfstc.org, (2014). Presumptive v. Confirmatory Tests. [online] Available at: http://www.nfstc.org/pdi/Subject02/pdi_s02_m02_01_a.htm [Accessed 09 Dec. 2014].

Rainn.org, (2014). Preserving and Collecting Forensic Evidence | RAINN | Rape, Abuse and Incest National Network. [online] Available at: https://www.rainn.org/get-information/aftermath-of-sexual-assault/preserving-and-collecting-forensic-evidence [Accessed 21 Dec. 2014].

Karl M. McDonald is a free lance writer specializing in the field of DNA. Karl has been working in the DNA testing industry for over six years and regularly contributes to various websites and blogs related to DNA & forensics as well as genetic disorders.