FTCoE In-Brief Series Looks at Physical Evidence and Sexual Assault

Recent headlines about cold cases solved through family trees and used soda cans have helped push the idea that the only evidence needed to solve any criminal case is a touch of DNA. That’s far from reality, and when it comes to sexual assault cases in particular, every piece of physical evidence collected can work together to build a case that will corroborate a victim’s account.

The National Institute of Justice’s Forensic Technology Center of Excellence recently released a three-part In-Brief series of reports on the importance of various types of physical evidence in sexual assault investigations. Found on the web here, Beyond DNA – Sexual Assault Investigations uses 6- to 8-page reports on physical, biological and toxicological evidence to bring law enforcement, policymakers, legal professionals and the public an overview of various types of physical evidence and how they may impact sexual assault investigations. In addition, the documents take a look at ongoing NIJ research and provide links to additional resources.

Rebecca Shute, FTCoE innovation analyst, says the idea to create the reports came out of the 2016 NIJ Forensic Science R&D Symposium: “The idea of investigating evidence beyond DNA is always discussed, but never in detail. DNA provides very valuable information, but it’s not always present in every case. When a sample is present and CODIS [Combined DNA Index System]-eligible, there’s only a hit about half the time. Even if DNA is present and there is a CODIS hit, it may not be probative if sexual contact is not disputed.”

In order to ensure accuracy from a legal as well as a forensic standpoint, FTCoE partnered with AEquitas, a nonprofit organization of former prosecutors that provides resources for investigations of gender-based violence and human trafficking. They collaborated on FTCoE’s first report in the Beyond DNA series, summarizing the types of physical evidence collected in investigations, and explaining how physical evidence can be used to corroborate victims’ accounts. Other reports in the series focused on body fluid identification and toxicology, both of which are used frequently in developing a case, Shute says.

“We wanted the audience of this series to be general,” Shute says. “It’s more for members of the general public who may be exposed to an investigation at some point in their lives, or for law enforcement officers working sexual assault scenes to encourage them to think about collecting evidence that isn’t strictly related to DNA. It’s not for forensic toxicologists or lab analysts.”

The FTCoE plans to promote the reports to those audiences through a social media campaign, with specific targets for Sexual Assault Awareness Month in April.

“Physical evidence is critical to understanding and communicating the events that transpired during a sexual assault. DNA can provide some but not all of the story; other types of physical evidence can provide unique and valuable information,” Shute says. “Biological evidence and toxicological evidence in drug-facilitated sexual assault cases, in particular, can ultimately lead to just resolutions for these crimes in ways that DNA evidence could not have.”

The FTCoE maintains a variety of resources related to sexual assault, which is a key initiative of the Center. Visit here.


Series Highlights

Key points from each of the reports follow.

Part I: The Role of Physical Evidence in Sexual Assault Investigations

Physical evidence may include:

  • Physical injuries such as bruising and lacerations. These can, for example, corroborate a victim account of a struggle or determine the location of the incident.
  • Digital evidence such as text messages, emails and cellphone records; also data from fitness trackers, cell phone apps and smart home devices. These can establish the whereabouts of the victim and the alleged perpetrator.
  • Impression evidence (e.g., fingerprints, shoeprints).
  • Trace evidence (e.g., hairs, fibers).
  • Other physical evidence (e.g., bedding and clothing).
  • Also DNA, blood and body fluids, and toxicology.

Part II: The Role of Biological Evidence in Sexual Assault Investigations

Biological evidence can be found on a victim, on a suspect or at the scene. It typically includes blood from injury or trauma, menstrual blood, saliva, semen, urine and vaginal fluid.

It may:

  • Indicate that sexual or physical contact may have occurred.
  • Demonstrate that force or restraint may have been used.
  • Support or refute victim testimony, such as the type of assault, the physical location and perpetrator characteristics. Note that while it may indicate sexual or physical contact occurred, it does not necessarily indicate a crime and its absence does not indicate no assault took place.

Part III: The Role of Toxicological Evidence in Sexual Assault Investigations

Toxicology testing detects the presence of drugs and toxins through, for example, blood, urine and hair. It can help establish whether a victim was incapacitated or significantly impaired. According to the Bureau of Justice Statistics, an estimated 39 percent of sexual assaults from 2005 to 2010 were what is known as alcohol and drug-facilitated sexual assault (DFSA).

Toxicological evidence can:

  • Help establish drug/toxicant concentration thresholds capable of impairing capacity to consent.
  • Help investigators understand gaps in victim recall.
  • Help corroborate or disprove a scenario. For example, toxicological evidence may be able to estimate a time window for drug exposure.

Note that toxicology reports from blood can provide more detail, but during a shorter timeframe; urine can provide evidence for a longer timeframe, but it is not as precise; and hair can provide an alternative for up to 90 days, but at a further reduction in detail. Also, any prescription or over-the-counter drugs taken by the victim can alter the profile.


Article photo: iStock.com/AndreyPopov, iStock.com/Vladyslav Bobuskyi