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Evidence Collection

Editor: Ashish Badiye Updated: 5/8/2023 6:15:23 PM


An estimated 1,197,704 violent crimes occurred nationwide in 2015, according to the Federal Bureau of Investigation's Uniform Crime Reporting Program. Violent crimes are determined according to a Hierarchy Rule: murder, non-negligent manslaughter, rape, robbery, and aggravated assault. The collection, preservation, and forensic analysis of the evidence with most crimes are often critical in determining a person's guilt or a person's innocence. The forensic exam is beneficial to law enforcement and the medical setting to provide a comprehensive medical forensic examination with the collection of evidence knowing the patient's body is the crime scene. Evidence must be identified, collected, packaged, secured, and maintained correctly, then released to Law Enforcement following a strict chain of custody rules so that it can be analyzed appropriately and used later in legal proceedings. When collecting evidence, the examiner must wear gloves at all times and change them often utilizing the clean technique. Following proper collection, handling, and storage of evidence will reduce the possibility of cross-contamination or degradation of DNA.[1][2]

Issues of Concern

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Issues of Concern

Trace Evidence

May consist of debris such as dirt, soil, sand, gravel, grass, leaves, twigs, adhesives and tape, fibers, glass, or bullet fragments.

When trace evidence is identified, the following steps in the collection of the evidence is outlined below:

  • Document and photograph the evidence
  • Properly secure the evidence by placing it in a paper bag or envelope
  • Close, seal, or tape the paper bag or envelope. The examiner must initial, date, and time across the sealed area
  • Label the bag or envelope with the patient's identifying information
  • Examiner must place signature, date, and time on the envelope[3]

Biological Evidence

May consist of blood, skin, hair, semen, saliva, and urine.

  • Swabs (cotton tip applicators) collected for biological evidence may include buccal, oral, skin, fingernail, bitemarks, perineal, perianal, vaginal, cervical os, penile, scrotum, rectal.
  • Hair collected is placed in an envelope.

The same process for packaging, securing, and maintaining the evidence as outlined above is used for the collection of trace evidence.[4][5]

Clothing Evidence

Clothing that is worn by an individual at the time of the crime often contains physical or biological evidence that must be preserved. If the patient is wearing the clothes they had on during the assault, all items can be considered evidence. If the patient is not wearing the clothes they had on during the assault, clean clothing put on later by the patient, such as underpants in the case of a sexual assault, may still contain bodily fluids other than the patient's. The patient's clothing must be handled and examined carefully to avoid loss of evidence. Each piece of clothing must be dried thoroughly if wet or damp. Each piece must be identified, labeled with the patient's identifying information, date, time, and examiner's initials. All stains or tears to the clothing must be documented. When these steps have been completed, each piece of clothing must be placed in separate bags to avoid cross-contamination. The clothing placed in the individual bags must be identified, labeled with the patient's identifying information, the examiner's signature, initials, date, and time. Each bag is then placed in a larger bag, properly labeled with the patient's identifying information, the examiner's signature, initials, date, and time.  When clothing is collected, it must be correctly identified, packaged, preserved, secured, and maintained until released to law enforcement with the proper chain of custody for further analysis at a forensic/crime laboratory.[6]

Injury to the Body

The forensic examiner will take a history from the patient to help guide in performing a detailed head-to-toe assessment to identify injury or findings to the patient's body. Injury or findings must be documented by taking photographs, measuring the injury utilizing measuring tools, and/or using age-specific body diagrams. The correct terminology must be used to describe injury and findings. For example, medical personnel confuses lacerations versus cuts. Lacerations are caused by blunt force trauma, and cuts are caused by sharp force trauma, usually by a sharp object.

It is critical to correctly identify the injury and the mechanism of the injury:

  • Bruises, abrasions, lacerations, swelling, redness, pain caused by blunt force trauma.
  • Blunt force trauma is usually a serious injury caused by a blunt object or impact with a blunt surface.
  • A bruise is an injury to the tissue, causing rupture of the small blood vessels and escaping blood into the tissue that causes discoloration.  Discoloration varies from red, purple, bluish, green, yellow, and brown.  
  • Abrasion is the rubbing or scraping of the surface layer of cells or tissue from an area of the skin or mucous membranes.
  • A laceration is a torn and ragged wound.
  • Swelling is an abnormal enlargement of tissue.
  • Redness is abnormal redness of the skin or mucous membranes due to capillary congestion (e.g., inflammation).
  • Pain is the physical feeling caused by disease, injury, or something that hurts the body.
  • Cuts are puncture wounds resulting from sharp force trauma or a type of projectile---Cuts indicate penetration with or as if with an edged instrument.
  • Puncture wound means to pierce with or as if with a pointed instrument or object. 

Again to emphasize, when possible, the examiner may use a camera, measuring tools, and age-appropriate body diagrams to document the medical forensic examination.

Keeping the Evidence Secure[7]

Collection, preservation, and securing evidence are critical from the time it is collected.  Completion of the chain of custody documentation is also critical. The chain of custody form must contain information about the evidence collected and must remain with the evidence until it is released to law enforcement.  The patient's identifying information with the date, time, Law Enforcement involved with the case number must be included.  Each person who has had contact or possession of a piece of evidence must be identified on the chain of custody form from the time it is collected and then released to Law Enforcement.  If the chain of custody documentation is incomplete, inaccurate, or omitted, it will cause the evidence to be inadmissible in a court of law.

Important Factors to Follow When Collecting Evidence[8][9]

Collect evidence correctly, preserve each specimen separately, use and change gloves often, avoid coughing or sneezing during the collection, use appropriate tools such as cotton-tipped applicators, sterile water, cardboard swab boxes, separate paper bags, and envelopes to prevent cross-contamination of samples collected.

Allow swabs to dry thoroughly, dry with cool air only, no heat, package in a vented swab container boxes or paper. Do not use plastic.  All these steps will preserve the integrity of the samples collected.

To maintain accurate identification, each sample must be labeled with the patient's identifying information--patient's legal name, date of birth, medical record number, date, time, and the examiner's signature.  

Clinical Significance

The forensic examiner must be knowledgeable about the medical forensic examination and the different types of evidence of why, when, where, and how to collect, preserve, maintain and release the evidence.

Enhancing Healthcare Team Outcomes

Many patients will present with a need for a medical forensic examination with the collection of evidence. Many professionals will be involved in the care of these patients; clinicians, nurses, advanced practice nurses, forensic nurse examiners, and other healthcare providers. The healthcare provider should have advanced training in the care and overall assessment of the patient. Ongoing education and training are important due to the ever-changing advances in treatment and technology and can be achieved by attending conferences, reviewing published research studies, and using current guidelines and recommendations. Each healthcare provider is an important member of the team to accomplish the best outcome for the patient and assist with future follow-up care and resources. Many patients will have law enforcement involved for investigative purposes and possible legal proceedings. The healthcare provider may be required to testify in a court of law at a later date, usually years later. A thorough examination must be performed, documentation completed, and the evidence collected at the time of the examination must be complete, accurate, and concise.



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Level 3 (low-level) evidence


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Level 2 (mid-level) evidence


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Level 3 (low-level) evidence


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Level 3 (low-level) evidence


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