Forensic Evidence and Criminal Justice Outcomes in Sexual Assault Cases

An NIJ-funded study explored injury and forensic evidence in sexual assault cases using data from different types of medical examiners, laboratories, and the police.

April 18, 2018

Victims undergo difficult forensic medical examinations with the hope of contributing evidence that can help bring assailants to justice. To improve the likelihood that suspects will be identified, arrested, and convicted, the criminal justice field is exploring investigative methods that can decrease the burden on victims and increase the prospects of collecting biological evidence.

One such study analyzed data from Massachusetts to explore the role of injury evidence and forensic evidence in sexual assault cases using data from medical providers, crime laboratories, and police. Researchers examined how the collected biological evidence and the type and frequency of injuries related to arrest. The timing of evidence collection and arrest also was taken into consideration. The results were then compared based on who collected the evidence and the age of the victims (child or adult).  

Researchers found that more than half of the victims had nongenital injuries and about one-third had documented genital injuries. The researchers noted that the identification on genital injuries could assist police in documenting evidence needed to meet probable cause standards. 

Sexual Assault Nurse Examiners (SANEs) were three times more likely than other medical examiners to document a genital injury. Researchers pointed out that this was perhaps because of their specialized training. It was difficult for the researchers to determine the impact of SANEs on criminal justice outcomes because of differences in the communities and populations at the 27 hospitals served by the Massachusetts SANE Program. However, they did note that SANE involvement in a sexual assault case could impact outcomes not examined in the current study, such as increased police investigatory activities[1] and increased conviction rates and sentence lengths [2].

In this study, biological evidence was found in 84.6 percent of cases in which laboratory testing was completed; the most common type found was semen (approximately half of the cases). There is no typical rate in which biological evidence is discovered in sexual assault cases, based on a review of prior research. Of the cases with biological evidence, a DNA profile was generated for 41 percent. A match was obtained in about half of the cases in which a profile was generated.

Semen was significantly more likely to be found in cases when additional swabbing (e.g., external genital, vaginal swabbing) was completed. This indicates the importance of basing forensic evidence collection on patient history to maximize the ability to yield biological evidence.

This study also examined sexual assault cases in which a police agency determined that a report was baseless or false and did not pursue it any further, referred to as “unfounding.” One-third of the 528 cases in this study were unfounded. Cases involving physical force and penetration were less likely to be unfounded. Victim loss of consciousness, however, was associated with a higher incidence of unfounding.

The odds of unfounding also increased if the forensic medical examination was performed more than 24 hours after the incident occurred. In the study sample, two-thirds of the victims underwent a forensic medical examination within 18 hours, one-quarter within 24 hours, and 94 percent within 72 hours of the assault.  Researchers hypothesized that delays in both reporting and performing an examination may be related to unfounding because delays may decrease the likelihood of finding evidence.

After the examination, nearly half of the kits arrived at the crime laboratory within seven days of the forensic medical examination, and 85 percent within 30 days of the forensic medical examination. Crime laboratories reported testing results within 30 days of the arrival of the kits at the lab for 35.4 percent of the cases and within 120 days for 88.6 percent of the cases. The median was 43 days.

Of the 315 incidents that were not unfounded, 130 (41.2 percent) resulted in an arrest. Researchers determined that the availability of biological evidence was not a factor in most arrests. If a suspect was arrested, the arrest occurred within one week of the assault for a majority of cases (81 percent) and generally occurred before the police received forensic evidence reports. Most arrests (almost 90 percent) took place prior to laboratory analysis.

The 26 cases of child sexual assault were examined separately in this study. Almost half involved victims who were 5yearsold or younger, and approximately 30 percent were male. Compared to adult cases, both genital and nongenital injuries were documented less frequently. None of the cases involving children were unfounded and almost half resulted in an arrest. Biological evidence of some kind was found in slightly more than half of all cases, and six cases resulted in the generation of a DNA profile.

The researchers concluded that while signs of injury and biological evidence may have a substantial impact on criminal justice outcomes, the impact appears to occur in relatively few cases. Thus research solely using broad case databases will remain limited.

The researchers offer recommendations for future research in this area, including: a larger case sample to account for more variables that could impact case processing; advanced statistical modeling that includes risk analysis; analysis of jurisdictional differences and case processing across the criminal justice and medical systems; and a comparison of how police and prosecutors use biological evidence compared to other types of evidence.

About This Article

The research discussed in the article was conducted by Theodore P. Cross, Megan Alderden, Alexander Wagner, Lisa Sampson, Brittany Peters, Meredith Spencer, and Kaitlin Lounsbury. This study was supported by funding from the National Institute of Justice, grant number 2011-WG-BX-0005, awarded to the University of Illinois at Urbana-Champaign.

This article is based on the final report, “Forensic Evidence and Criminal Justice Outcomes in a Statewide Sample of Sexual Assault Cases” (pdf, 220 pages).

Cite This Article

National Institute of Justice, “Forensic Evidence and Criminal Justice Outcomes in Sexual Assault Cases,” Month DD, 2018, NCJ 248254, NIJ.gov: https://nij.gov/topics/law-enforcement/investigations/sexual-assault/Pages/forensic-evidence-and-criminal-justice-outcomes-in-sexual-assault-cases.aspx

Notes

[note 1] Campbell, R., D. Bybee, K.D. Kelley, E.R. Dworkin, and D. Patterson. “The Impact of Sexual Assault Nurse Examiner (SANE) Program Services on Law Enforcement Investigational Practices: A Meditational Analysis.” Criminal Justice and Behavior 39 (2012): 169-184.

[note 2] Crandall, C., and D. Helitzer. Impact Evaluation of a Sexual Assault Nurse Examiner (SANE) Program (pdf, 129 pages). Washington, DC: U.S. Department of Justice, Office of Justice Programs, National Institute of Justice, 2004. NCJ 203276.

Date Created: April 18, 2018