Various types of physical evidence can be collected in a sexual assault investigation to help establish the facts of the assault, identify or eliminate suspects, and corroborate or dispute statements. These can generally be categorized as follows:

From the Victim:

• Biological Evidence:
  • Swabs: Vaginal, anal, oral, and penile swabs to collect semen, saliva, blood, or other bodily fluids.
  • Hair Samples: Head and pubic hair combings and pulled hairs for comparison.
  • Blood and Saliva Samples: For the victim’s DNA profile to differentiate it from potential perpetrator DNA.
  • Fingernail Scrapings: To collect any skin cells, hair, or fibers from a potential assailant.
  • Clothing: Garments worn during the assault, which may contain biological fluids, hair, fibers, or other trace evidence.
  • Bedding/Linens: If the assault occurred on a bed, these items can contain biological fluids, hair, or fibers.
  • Foreign Material: Any debris, leaves, or other substances found on the victim’s body or clothing.
• Physical Injuries:
  • Photographs: Documentation of any bruises, cuts, abrasions, bite marks, or other injuries.
  • Medical Examination Records: Detailed notes by medical personnel about injuries observed.

From the Suspect:

• Biological Evidence:
  • Swabs: Penile, oral, and other swabs as indicated.
  • Hair Samples: Head and pubic hair samples for comparison.
  • Blood or Buccal Swabs: For the suspect’s DNA profile.
  • Clothing: Garments worn during the assault, which may contain the victim’s biological material or other trace evidence.
• Physical Injuries:
  • Photographs: Documentation of any scratches, bruises, or injuries that could be related to the assault.

From the Crime Scene:

• Biological Evidence:
  • Swabs: Of surfaces where the assault may have occurred to collect biological fluids.
  • Hair and Fiber Samples: Collected from the scene.
  • Bloodstains or other Body Fluid Stains: Documented and collected.
• Trace Evidence:
  • Fibers: From clothing, carpets, or other materials.
  • Hairs: Not belonging to the victim.
  • Soil or Plant Matter: If the assault occurred outdoors.
• Impression Evidence:
  • Fingerprints and Palm Prints: From surfaces the suspect may have touched.
  • Footprints or Shoeprints: If applicable.
• Weapons or Instruments: If a weapon or other instrument was used in the assault, it should be collected and analyzed for biological or trace evidence.
• Condoms or Lubricants: If used, these can contain biological evidence.

When Might Evidence Not Be of Probative Value?

Physical evidence collected in a sexual assault investigation might not be probative (i.e., not tending to prove or disprove a fact at issue) in several circumstances:

• Lack of Chain of Custody: If the evidence is not properly documented, collected, sealed, and tracked from the moment it is obtained until it is presented in court, its integrity and reliability can be questioned, rendering it less probative or inadmissible.
• Contamination: If evidence is mishandled or improperly stored, it can become contaminated, making any subsequent analysis unreliable and the evidence less valuable.
• Timing Issues: Biological evidence, particularly DNA, can degrade over time or be washed away, making it less likely to yield useful results if a significant amount of time has passed since the assault. For instance, semen may not be detectable after a certain period, especially if the victim showered.
• Lack of Relevance: The evidence collected might not be relevant to the specific allegations of the assault. For example, the presence of the suspect’s DNA might be explained by a prior consensual encounter and not the assault in question.
• Insufficient Quantity or Quality: The amount of biological material recovered might be too small or too degraded to yield a usable DNA profile.
• Alternate Explanations: There might be innocent explanations for the presence of certain evidence. For example, finding the suspect’s hair in the victim’s home if they were known to each other and had visited previously.
• No Connection to the Assault: Evidence found might be unrelated to the assault itself. For example, finding fingerprints that belong to first responders or medical personnel.
• Consent is the Central Issue: In cases where the act of sexual contact is not disputed, but the issue is consent, physical evidence confirming contact may be less probative on the specific element of non-consent. However, it can still corroborate the victim’s account of the events.

It’s crucial to remember that the probative value of evidence is ultimately determined by the court. Investigators and forensic analysts work to collect and analyze evidence meticulously to maximize its potential to contribute to the investigation and any subsequent legal proceedings.