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

NCJ Number
Date Published
January 2019
8 pages
This second of a three-part series on the role of physical evidence in sexual assault cases, in addition to DNA, addresses biological evidence as one category of such physical evidence.
The introductory section notes that physical evidence collection, submission, and analysis can be an important and even necessary means of reconstructing some of the events that occurred during a sexual assault, even if a DNA profile is developed. In focusing on biological evidence, this paper addresses such evidence as blood (from injury or trauma), menstrual blood, saliva, semen, urine, and vaginal fluid. Additional materials that contain DNA, such as hair and skin cells, may be collected in sexual assault casework. This report focuses on body fluids, i.e., evidence collected as part of a sexual assault kit (SAK) at the crime scene. Up to 88 percent of cases with biological evidence are sent for DNA testing; however, not all of these evidentiary items will produce DNA profiles with sufficient quality to be uploaded into the Combined DNA Index System (CODIS); however, the value of body fluids is not limited to being a source for DNA, since it can provide details about events that occurred during a sexual assault. Some potential non-DNA uses of biological evidence include to indicate that sexual or physical contact may have occurred; to establish that force or restraint may have been used; and to assist in corroborating or disproving a scenario. In the course of an investigation, biological evidence may be collected by crime-scene professionals, law enforcement officers, laboratory analysts, and forensic healthcare professionals such as sexual assault nurse examiners or sexual assault forensic examiners and medical examiners. In a sexual assault cases, biological evidence may be collected from the individual who reported the sexual assault, suspects, and/or the crime scene.

Date Published: January 1, 2019