In-Brief Report Series: Beyond DNA – Sexual Assault Investigations

In-Brief Report Series: Beyond DNA – Sexual Assault Investigations


January 2019


The National Institute of Justice (NIJ) is committed in their efforts to support scientific advancement, evidence-based practices, and community awareness of our Nation’s sexual assault response. As NIJ’s Director, Dr. David B. Muhlhausen, indicated, “our nation’s forensic laboratories have the ability to find and test smaller and smaller amounts of crucial evidence and get quality results for cases that years ago would have been unattainable” [1]. NIJ’s numerous sexual assault response resources, including the National Best Practices for Sexual Assault Kits: A Multidisciplinary Approach, are summarized in this NIJ Director’s Message [1, 2].

Sexual assault remains prevalent in the United States, with an average of 300,000 cases reported to law enforcement each year [3]. However, another 600,000 go unreported [4]. The circumstances of and trauma resulting from a sexual assault can pose a challenge to investigators. For example, witnesses are not always present; the impact of trauma or incapacitating substances, such as alcohol, may affect the victim’s ability to recount details of the incident; and frequently, corroborating evidence is limited.

DNA evidence, while valuable, is not always probative or present in every case: many DNA samples do not meet the quality standards required to be uploaded into CODIS (38% of profiles were found to be ineligible as noted from recent NIJ-supported research [5]). Even in cases where a DNA profile is present and is CODIS-eligible, a CODIS hit occurs only about half of the time [5]. Additionally, a DNA profile may provide limited probative value in situations where sexual contact is not disputed. Thus, many types of additional physical evidence play a critical role in the investigation and prosecution of sexual assault cases.

Physical evidence collection, submission, and analysis can be an effective and necessary means of reconstructing at least some of the events that occurred during a sexual assault. Physical evidence provides value to investigations even if a DNA profile is developed and probative, as it can be used to corroborate and supplement a greater understanding of the circumstance and make a stronger case. This three-part Beyond DNA In-Brief series highlights types of physical evidence that can provide crucial information about a sexual assault, so that key stakeholders in the criminal justice community ultimately obtain just resolutions for these crimes.

Beyond DNA: The Role of Physical Evidence in Sexual Assault Investigations

“Based on our findings, jurors were more likely to find a defendant guilty than not guilty even without scientific evidence if the victim or other witnesses testified, except in the case of rape.” —Honorable Donald E. Shelton, The 'CSI Effect': Does It Really Exist?, National Institute of Justice (NIJ)

Beyond DNA: The Role of Biological Evidence in Sexual Assault Investigations

“Sexual assault evidence should be evaluated holistically. The identification of the type of biological fluid may further substantiate and clarify how events took place.” -Dr. Patricia Melton, RTI International

Beyond DNA: The Impact of Toxicological Evidence in Sexual Assault Investigations

"Because of the effects that CNS depressants can have on memory and the subsequent reporting of suspected DFSA by potential victims, the true prevalence of this crime may never be fully realized." - Marc LeBeau, FBI Laboratory


The NIJ and the FTCOE provide resources for sexual assault response, including:

Additional Resources

1. Muhlhausen D.B. (2018, April). Director’s Corner: Responding to Sexual Assaults. Washington, DC: U.S. Department of Justice, Office of Justice Programs, National Institute of Justice. Retrieved from .
2. National Institute of Justice. (2017, August 8, 2017). National Best Practices for Sexual Assault Kits: A Multidisciplinary Approach. NCJ 250384. Washington, DC: U.S. Department of Justice, Office of Justice Programs, National Institute of Justice. Retrieved from: .
3. Morgan, R. E., & Kena, G. (2017, December). Criminal victimization, 2016. Washington, DC: U.S. Department of Justice, Office of Justice Programs, Bureau of Justice Statistics. Retrieved from  
4. Rape, Abuse & Incest National Network. (2018). The criminal justice system: Statistics. Retrieved from 
5. Waltke, H., LaPorte, G., Weiss, D., Schwarting, D., Nguyen, M., & Scott, F. (2017). Sexual Assault Cases: Exploring the Importance of Non-DNA Forensic Evidence. National Institute of Justice Journal, 279.

Funding for this Forensic Technology Center of Excellence report was provided by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.

The opinions, findings, and conclusions or recommendations expressed in this report are those of the author(s) and do not necessarily reflect those of the U.S. Department of Justice.

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