After an evening of hanging out with friends, a 20-year-old woman decided to get a ride home with her ex-boyfriend. They had broken up several months before but had remained friendly with each other. During the drive, the young man started talking about how they should get back together because he missed the relationship they once had. However, she was not interested and wanted to remain friends.
Only blocks from her home, the man stopped the car and suddenly turned violent. Grabbing her neck, he began to force himself on her. As he ripped off her clothes, she managed to grab a small pocket knife from her purse, but he took the knife from her and broke it. He then dragged her by the legs out of the car and raped her in a nearby wooded area. Afterwards, he stole her credit cards and drove away. The woman managed to walk to her home and called the police to report the rape. She was brought to the hospital, where she was interviewed, photographed, and examined for several hours. Evidence was collected for a sexual assault kit (SAK).
To many, this would seem like a clear-cut case of sexual assault. However, a case is not determined by what one believes, but rather by what the investigation shows and what can be proved.
When the police spoke with the young man, he described a very different series of events. He claimed that he and his ex-girlfriend had a fun evening at the party and that she came on to him and wanted to get back together. He admitted to taking some drugs that evening and thought he blacked out briefly. When he woke up, he claimed that his ex-girlfriend was on top of him and they had consensual rough sex. He said their clothes were everywhere, and he must have accidently taken her credit cards when he gathered his things. He denied ever handling a knife.
So what really happened that evening? In a case like this of “he said, she said,” investigators look to the forensic evidence to help them piece together what may have actually happened. The investigation and exploration of the totality of the evidence collected are critical to unravelling the allegations and discerning whether charges can be filed.
DNA Is Not Always Probative or Present
DNA analysis has had an unprecedented impact on the criminal justice system. It has propelled investigations forward and made charging those alleged to have committed the crime easier. Science can now provide focus or direction to an investigation, help develop a case theory, and clear suspects or those wrongfully convicted with more certainty. As a result, the criminal justice community has become highly reliant on DNA analysis.
Many believe DNA analysis is the death knell for most criminal defendants, and juries and lawyers alike expect to see DNA evidence presented during a trial. It has been reported that 72 percent of jurors anticipate seeing DNA in a sexual assault trial and that juries are 33 times more likely to convict when presented with DNA evidence. This raises serious concerns, as the need to provide probative DNA evidence in sexual assault cases has become increasingly more important if a prosecutor hopes to secure a conviction.
But what happens in a “he said, she said” case like the one described above, where the alleged suspect is not a stranger and, in fact, admitted to having sexual intercourse? In a random sampling of 602 reported rapes, 36.2 percent were among intimates or family members and 42.7 percent were friends or acquaintances. In such cases where the suspect and victim are acquainted, consent is pivotal to determining whether a crime was committed, and the presence of the suspect’s DNA may not necessarily be informative.
Or what about cases in which no DNA is found? Recently, a great deal of attention has been placed on testing SAKs, especially those collected years ago and never submitted to a forensic laboratory. Although testing SAKs for DNA is important, the reality is that DNA is sometimes not found or is not eligible for entry into the Combined DNA Index System (CODIS), which is composed of databases maintained by the Federal Bureau of Investigation that allow DNA profiles to be compared to one another. For example, to be uploaded into CODIS, DNA profiles must meet certain quality standards, and sometimes the DNA is old, degraded, not in sufficient quantity, or otherwise unviable. Additionally, the sample may not be directly probative (such as in cases in which the person alleged to have committed the crime admitted having sexual contact). Based on NIJ’s SAK-related projects (see exhibit 1), DNA profiles that were of sufficient quality for CODIS upload were obtained in only 38 percent of more than 7,000 SAKs submitted for DNA testing. Also, performance metrics collected from NIJ’s Solving Cold Cases With DNA program showed that about 48 percent of the cases with tested biological evidence yielded any DNA profile. NIJ’s results are consistent with other national findings. For example, a recent South Dakota SAK project that tested 504 kits yielded only 254 DNA profiles, and half of the 3,542 kits tested in a Colorado project yielded DNA profiles.
As new and emerging technologies advance across the criminal justice system and provide necessary links for locating and apprehending assailants, criminals continue to learn about forensic science techniques and have started to “get smart.” Many individuals who commit sex offenses, for example, now use gloves, masks, and condoms, and some even have a victim shower before they leave a scene — all in the hope of thwarting law enforcement’s ability to collect potential DNA evidence. Take, for example, the case of Colorado serial rapist Marc O’Leary, who committed several sexual assaults in multiple jurisdictions. He ordered women to shower and brush their teeth, and he took the bedding and clothing with him. However, he executed his crimes with the same modis operandi, leaving behind shoe prints, glove pattern evidence, and other non-DNA evidence that was used to connect him to the crime scenes.
Number of SAKS Tested
Number of CODIS Entries
% of Profiles Eligible for CODIS Entry
CODIS Hits/ CODIS Entries (%)
CODIS Hits/Total Number of SAKS (%)
|FBI (as of 1/5/2017)[^^]||1,584||808||51%||306||38%||19%|
|Marshall (as of 10/5/2016)[^^^]||588||149||25%||39||26%||7%|
[note *] Joseph Peterson et al., “Sexual Assault Kit Backlog Study,” Final report to the National Institute of Justice, grant number 2006-DN-BX-0094, June 2012, NCJ 238500.
[note **] Rebecca Campbell et al., “The Detroit Sexual Assault Kit (SAK) Action Research Project (ARP),” Final report to the National Institute of Justice, grant number 2011-DN-BX-0001, December 2015, NCJ 248680.
[note ***] M. Nelson, Analysis of Untested Sexual Assault Kits in New Orleans, 2012, Washington, DC: U.S. Department of Justice, National Institute of Justice; FBI-funded interagency agreement with NIJ 2013MUR6019.
[note ^] William Wells, Bradley Campbell, and Cortney Franklin, “Unsubmitted Sexual Assault Kits in Houston, TX: Case Characteristics, Forensic Testing Results, and the Investigation of CODIS Hits,” Final report to the National Institute of Justice, grant number 2011-DN-BX-0002, April, 2016, NCJ 249812.
[note ^^] Learn more about the NIJ-FBI Sexual Assault Kit Partnership.
[note ^^^] For more information, go to http://hpdwv.com/initiatives/sexual-assault-kit-testing-project/.
The Value of Non-DNA Evidence
In cases in which probative DNA evidence is not readily available or offers little or no meaning to the allegations being made, an accumulation of non-DNA forensic evidence can be what ultimately leads to a successful conviction.
A wealth of other forensic evidence may be invaluable in sexual assault investigations; some examples are trace evidence (e.g., hairs, fibers, glass, paint, or soil), toxicology, cellphone and digital forensics, and impression and pattern evidence (e.g., fingerprints, shoe prints, tire marks, and handwriting). One study showed that in addition to bodily fluids, fingerprints and hairs are the most common types of physical evidence collected and examined in sexual assault casework. The Bureau of Justice Statistics also reported that from 2005 through 2010, individuals committing sexual assault were armed with a gun, knife, or other weapon in 11 percent of rape or sexual assault victimizations. All of these types of non-DNA forensic evidence can be used to identify a suspect, associate a suspect with a victim, associate a suspect with a crime scene, and corroborate other evidence.
Based on the evidence identified and collected during the sexual assault investigation in our case example, the knife was tested and contained prints of both the victim and the suspect, even though the suspect denied handling the knife. The young woman had no alcohol in her system, and the medical exam showed she had cuts, bruises, and tears to her body and genitals — 33 documented injuries. Her clothing was torn and her pants zipper was broken. Toxicology results revealed that the suspect tested positive for methylenedioxy-methamphetamine (MDMA, commonly known as Ecstasy), a drug that is known to produce feelings of increased energy, pleasure, and distorted sensory and time perception. The investigation also revealed that the suspect sent the victim text messages in the days after the assault, even though he denied having any contact with her.
Therefore, when DNA is not available or not probative, other forensic evidence can help establish the facts. The most important take-away is that a case should be developed using the totality of the evidence rather than relying solely on DNA, which allows one to recreate an entire series of events; corroborate or refute testimony from the victim, suspect, or other witnesses; and ultimately include or exclude a potential suspect. Based on the accumulated evidence described in this case scenario, criminal charges would likely result, as there is evidence showing injury and violence, corroboration of the victim’s account of the attack, and evidence that would disprove aspects of the suspect’s version of events.
Prosecutors also rely on scientific evidence to establish and prove their cases during prosecution. Research has shown that “… analysis of forensic evidence was associated with [increased] case referrals to prosecutors, [and] charges filed ….” Evidence from a medical forensic exam can be key in the prosecution of a sexual assault case. A study conducted in 1999 found a relationship where the victims’ injuries were seen as one of the most significant predictors in the decision to prosecute in nonstranger cases. The presence of injuries seemed to influence a prosecutor’s decision-making, as the documented appearance of violence makes it more difficult to assert consent.
The presence of forensic evidence also strengthens the likelihood of conviction at trial and has been associated with harsher sentences. Prosecutors are better able to recreate events and illustrate a theory to a jury by connecting testimonial evidence and forensic evidence. More specific to sexual assault cases, research has indicated that cases with physical evidence were more likely to lead to arrest, be referred to the prosecutor, be charged, and result in conviction than cases without evidence. Sometimes the availability or admission of forensic evidence, merely to show its existence, can be essential as well. Regardless of the context or support the evidence may offer to a case, juries continue to expect personally identifying forensic evidence; for example, Ric Ridgway, chief prosecutor for the 5th Judicial Circuit in Central Florida, received feedback from jurors after an acquittal asserting, “Well, there wasn’t any DNA or fingerprints.”
The Need for Research and Innovative Non-DNA Forensic Methods
Countless types of forensic evidence are used to investigate and prosecute thousands of crimes annually. According to the Bureau of Justice Statistics, in 2014 the nation’s 409 crime labs received an estimated 3.8 million requests for forensic services. Only 9 percent of these requests were for forensic biology casework such as from a crime scene (which includes DNA testing), and 24 percent were for DNA analysis of reference samples collected from those convicted and arrested that were then added to the national database. This means 67 percent of the total requests were solely for non-DNA forensic analysis.
Exhibits 2 and 3 illustrates the types of evidence analysis requested from publicly funded laboratories between 2009 and 2014. Clearly there is a demand for non-DNA forensic evidence. Toxicology testing, or the identification of drugs or other chemicals in the human body, was the third most requested of all forensic evidence, after forensic DNA sample testing. Controlled substance analysis of drugs or chemicals regulated by the government, such as cocaine, heroin, marijuana, or certain prescription drugs, was first.
Toxicological analysis has become critical in the prosecution of drug-facilitated sexual assault cases as another way to nullify an assertion of consent. To further advance science and ensure that evidence can be identified and used appropriately, NIJ supports and funds a diverse portfolio of forensic science research to develop highly discriminating, accurate, reliable, cost-effective, and rapid methods for the identification, analysis, and interpretation of physical evidence for criminal justice purposes.
See “Drug-Facilitated Sexual Assaults.”
|Type of request||Number, 2009||Percent, 2009||Number, 2014||Percent, 2014|
|Forensic biology casework||260,000||6||333,000||9|
|Forensic biology from samples taken from individuals convicted/arrested||1,053,000||26||908,000||24|
|Type of request||2009 Number||2009 Percent||2014 Number||2014 Percent|
|Forensic biology casework||239,000||6||296,000||8|
|Forensic biology from samples taken from individuals convicted/arrested||1,027,000||27||904,000||25|
Totals exclude requests outsourced to other labs. The number of requests completed in 2009 and 2014 exceeded the number of requests received during that year for certain disciplines because the completed requests included some requests received prior to that year. Numbers are rounded to the nearest thousand. Detail does not sum to total due to rounding.
"--" indicates less than 0.5 percent.
Source: Bureau of Justice Statistics, Census of Publicly Funded Forensic Crime Laboratories, 2009 and 2014.
Fingerprint evidence can be instrumental when trying to place a person at a crime scene, such as from the knife used during the assault in the opening case scenario. As seen in exhibits 2 and 3, requests for fingerprint analysis have only increased. Other than DNA, fingerprints are one of the most common types of evidence that can link a person to an assault. NIJ has a rich research and development portfolio focused on new technologies related to the development of latent prints, as well as studies related to the accuracy and reliability of fingerprint examinations.
See “What You Can’t See Might Solve the Case”
In certain cases of sexual assault, chemical examination of condom lubricants may also prove surprisingly valuable, as many assailants commit serial crimes and routinely use condoms to avoid leaving DNA evidence. NIJ recently funded a project at the University of Central Florida to improve the characterization and classification of condom lubricants recovered in sexual assault cases and build databases of lubricant mass spectra and infrared spectra that will be available for use in casework. This type of analysis can help determine if the person used a condom and, in some cases, forensic scientists can compare the lubricant recovered from the victim with condoms seized from the suspect.
Additionally, analyzing the various materials used during an assault can provide important information; for example, physically matching a piece of tape collected from a bound victim with evidence recovered from a suspect. Recognizing that duct tape is commonly used in abductions, homicides, and the construction of explosive devices, NIJ provided funding for researchers at the University of California, Davis to perform a statistical evaluation on matching the torn and cut ends of duct tape. They examined 1,800 torn tape specimens and 400 cut tape specimens and concluded that the mean accuracy for correctly matching specimens ranged from 98.58 to 100 percent for torn tape and from 98.15 to 99.83 percent for cut tape. NIJ also awarded Florida International University a grant to evaluate and validate the scientific reliability of chemical methods for profiling tapes. Using a collection set of more than 250 tapes (duct and electrical), researchers are applying rigorous analytical methods to examine the variations within and between rolls of tape to understand the relation to tape manufacturing and distribution.
Finally, body fluid identification of stains (such as differentiation of semen, saliva, vaginal fluid, and menstrual blood) can be critical in identifying probative evidence and corroborating the events of an assault. Serological methods used for body fluid identification can provide more meaningful information about the nature of the crime. Even in the absence of definitive DNA results, confirmation for the presence of body fluids — semen or saliva, for example — in a victim or on a particular piece of evidence may prove significant in building a case or corroborating events. This evidence may provide a prosecutor with the source attribution information needed to connect specific forensic evidence with testimonial accounts. For example, if a victim asserts that an assailant bit her neck and ejaculated on her jeans, the body fluid identification process would allow one to assert that the fluid collected from the victim’s neck was saliva and biological material on the victim’s clothing was, in fact, semen and not from casual contact. Body fluid evidence can also be significant in instances where a suspect states that the presence of blood was a result of consensual sex with a partner in menses. In these cases, identification of the stain as venous blood might refute this claim and instead support that a violent act had occurred.
As with all science, body fluid identification can be advanced. For example, the power to more accurately differentiate one body fluid from another may be increased, meaning that presumptive or preliminary identifications can be moved toward more confirmatory conclusions. Also, the time and effort required to complete testing could be decreased and sample consumption and destruction could be minimized. Currently, all commonly used testing methods involve exhausting a portion of the evidence sample to test for each body fluid presumed to be present. NIJ continues to support and fund innovative research to address the need for new tools to better identify body fluids while minimizing the consumption of evidence.
See “Body Fluid Identification.”
Empowering Criminal Justice Stakeholders and Victims Through Forensic Science
Forensic evidence as collected and analyzed is unbiased, as the science does not judge. Science is about revealing facts. For example, finding a fingerprint at the scene of a crime does not imply guilt or innocence; it is offered only to identify that a person was at a particular location or touched a particular item at some point, not whether he or she committed a crime. Any inferences drawn depend on the criminal justice practitioner using the information. Solving sexual assault crimes — bringing rapists to justice and supporting victims — is much more complicated than simply testing SAKs.
All aspects of criminal justice practice — from the initial investigation through adjudication — can benefit from DNA and non-DNA forensic evidence. However, processing and analyzing forensic evidence in a timely and efficient manner are critical. Delays in testing make the use of forensic evidence impractical during the investigative phase; therefore, many law enforcement officers do not realize the full potential of all forensic evidence as a tool for developing new leads in investigations. For example, NIJ’s National Best Practices for Sexual Assault Kits: A Multidisciplinary Approach emphasizes the importance of the identification, collection, and preservation of all evidence, not just DNA, from victims and crime scenes. The forensic science community has a responsibility to provide investigators with the answers they need, when they need them. As technology and testing methods advance, new tools may become available, throughput will increase, and the benefits of forensic analysis on various types of evidence may be better realized earlier in investigations.
Within this complex process, the forensic evidence itself affects many of the decision points, including but not limited to decisions to arrest, referral for and filing of charges, plea arrangements, and court outcomes. The justice system has come to rely a great deal on various types of evidence to help link a suspect to a crime scene and to the victim, but often in sexual assault cases, forensic evidence is also used to corroborate or refute statements of fact. That is, the findings from forensic testing are also used to substantiate a victim’s or suspect’s account. In rape cases where a DNA profile from a suspect is recovered, the findings may affirm the victim’s testimony and even empower the victim, because their story is now corroborated.
It is critical to provide increased training for law enforcement, prosecutors, and judges on the application and scientific validity of forensic evidence. In addition, increasing the overall capacity of our nation’s laboratories to process all forensic evidence and advancing policies and best practices for the collection and processing of evidence are crucial to the timely and accurate testing and delivery of results to the law enforcement and judicial communities. Furthermore, the criminal justice system needs sound research that not only advances current forensic practice but also substantiates the existing validity of forensic evidence analyses, so all involved can be assured that the evidence being proffered against someone is sound. Evidence has a voice; we need to ensure that science continues to be just and unbiased and that those who are listening are trained and accountable.
For More Information
Read NIJ’s “National Best Practices for Sexual Assault Kits: A Multidisciplinary Approach.”
Read about the NIJ-FBI sexual assault kit partnership.
Learn more about rape and sexual assault.
Read about sexual assault on campus.
Read four brochures to help address issues with unsubmitted sexual assault kits in your jurisdiction.
About This Article
This article was published as part of NIJ Journal issue number 279, April 2018.
[note 1] “Many attorneys, judges, and journalists have claimed that watching television programs like CSI has caused jurors to wrongfully acquit guilty defendants when no scientific evidence has been presented. The mass media quickly picked up on these complaints. This so-called effect was promptly dubbed the ‘CSI effect,’ laying much of the blame on the popular television series and its progeny.” Donald E. Shelton, “The ‘CSI Effect’: Does It Really Exist?” NIJ Journal 259 (March 2008): 1-7, NCJ 221500.
[note 2] Donald E. Shelton, Young S. Kim, and Gregg Barak. “A Study of Juror Expectations and Demands Concerning Scientific Evidence: Does the ‘CSI Effect’ Exist?” Vanderbilt Journal of Entertainment and Technology Law 9 (2006): 331-368.
[note 3] Michael Briody, “The Effects of DNA Evidence on Sexual Offence Cases in Court,” Current Issues of Criminal Justice 14, (2002): 159.
[note 4] Joseph Peterson et al., “Sexual Assault Kit Backlog Study,” Final report to the National Institute of Justice, grant number 2006-DN-BX-0094, June 2012, NCJ 238500.
[note 5] Of course, this should not preclude investigators from obtaining a DNA sample from the suspect to upload into the FBI’s Combined DNA Index System (CODIS) database, which may help to establish whether the suspect has a history of “acquaintance rapes” or has committed other unsolved crimes.
[note 6] As of January 2017, CODIS requires 20 core loci for DNA data to be included in the DNA database. Federal Bureau of Investigation, “Frequently Asked Questions on CODIS and NDIS,” February 17, 2017. Basic criteria for a CODIS entry are as follows: documentation that a crime was committed, a documented request to collect consensual partners/elimination samples, the evidence produced a DNA profile that was foreign to the victim, and the DNA profile meets the FBI’s data quality requirements.
[note 7] An assailant’s DNA profile may be probative in a sexual assault case where consent is at issue, if the DNA profile links the person to other similar crimes.
[note 8] Studies represent unique projects with unique circumstances and should not be compared against one another; rather, the results are an illustration of consistency that less than 50 percent of SAKs produce CODIS-eligible profiles.
[note 9] Cases reviewed within NIJ’s Cold Case program are not limited to sexual assaults.
[note 10] Seth Augenstein, “South Dakota Clears Rape Kit Backlog — 16 Percent CODIS Hits,” Forensic Magazine (January 23, 2017).
[note 11] Noelle Phillips, “Colorado Eliminates Backlog of Rape Test Kits, Identifies Suspects in Hundreds of Old Cases,” The Denver Post, July 16, 2016.
[note 12] T. Christian Miller and Ken Armstrong, “An Unbelievable Story of Rape>,” New York: ProPublica and The Marshall Project, 2015.
[note 13] Joseph L. Peterson, Steven Mihajlovic, and Michael Gilliland, Forensic Evidence and the Police: The Effects of Scientific Evidence on Criminal Investigations, Washington, DC: U.S. Government Printing Office, 1984; cited in Donald Johnson et al., “Use of Forensic Science in Investigating Crimes of Sexual Violence: Contrasting Its Theoretical Potential With Empirical Realities,” Violence Against Women 18 no. 2 (2012): 193-222.
[note 14] Michael Planty et al., Female Victims of Sexual Violence, 1994-2010, Special Report, Washington, DC: U.S. Department of Justice, Bureau of Justice Statistics, March 2013, NCJ 240655.
[note 15] Specific charges would be dependent on state laws.
[note 16] Tasha A. Menaker, Bradley A. Campbell, and William Wells, “The Use of Forensic Evidence in Sexual Assault Investigations: Perceptions of Sex Crimes Investigators,” Violence Against Women 23 no. 4 (2017): 399-425.
[note 17] Ibid.
[note 18] Joseph Peterson et al., “The Role and Impact of Forensic Evidence in the Criminal Justice Process,” Final report to the National Institute of Justice, grant number 2006-DN-BX-0094, September 2010, NCJ 231977.
[note 19] Ibid.
[note 20] Lauren Ritchie, “'Tech Effect' Has Juries Seeking Scientific Proof,” Sun Sentinel (Fort Lauderdale, FL), July 10, 2011.
[note 21] Matthew R. Durose, Andrea M. Burch, Kelly Walsh, and Emily Tiry, Publicly Funded Forensic Crime Laboratories: Resources and Services, 2014, Washington, DC: U.S. Department of Justice, Bureau of Justice Statistics, November 2016, NCJ 250151.
[note 22] “Awards Related to Forensics and Research and Development,” National Institute of Justice.
[note 23] Ibid.
[note 24] Frederic A. Tulleners and Jerome V. Braun, “The Statistical Evaluation of Torn and Cut Duct Tape Physical End Matching,” Final report to the National Institute of Justice, grant number 2009-DN-BX-K235, July 2011, NCJ 235287.
[note 25] “Awards Related to Forensics and Research and Development,” National Institute of Justice.
[note 26] NIJ has supported research at the University at Albany (SUNY), which seeks to develop nondestructive optical methods for rapidly and effectively differentiating between body fluid stains in forensic contexts. Igor K. Lednev, “Raman Spectroscopy for Analyzing Body Fluid Traces: Stain Aging, Differentiation Between Races, Genders, and Species,” University at Albany, SUNY, Department of Chemistry, Albany, NY: The Research Foundation of SUNY, 2015.
[note 27] Kevin J. Strom et al., “The 2007 Survey of Law Enforcement Forensic Evidence Processing,” Final report to the National Institute of Justice, grant number 2007F_07165, October 2009, NCJ 228415.
[note 28] Rebecca Campbell et al., “The Detroit Sexual Assault Kit (SAK) Action Research Project (ARP),” Final report to the National Institute of Justice, grant number 2011-DN-BX-0001, December 2015, NCJ 248680.