Evidence Collection

Article Author:
Deborah Kleypas
Article Editor:
William Gossman
1/30/2019 9:06:10 AM
PubMed Link:
Evidence Collection


In 2015, an estimated 1,197,704 violent crimes occurred nationwide, 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. With most crimes, the collection, preservation and forensic analysis of the evidence 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 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

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 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 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 such as underpants in the case of a sexual assault may still contain fluid body evidence for analysis. 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 initials of the examiner. 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 contamination. The clothing placed in the individual bags must be identified, labeled with the patient's identifying information, the examiners signature, initials, date, and time. Each bag is then placed in a larger bag which is properly labeled with the patient's identifying information, the examiners 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 and/or using age-specific body diagrams. It is very important that the correct terminology is 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 collision with a blunt surface
  • Bruise is an injury transmitted through unbroken skin to underlying tissue causing rupture of the small blood vessels and escape of blood into the tissue with resulting discoloration
  • Abrasion is the rubbing or scraping of the surface layer of cells or tissue from an area of the skin or mucous membranes
  • Laceration is a torn and ragged wound 
  • Swelling is abnormal bodily protuberance or localized enlargement
  • Redness is abnormal redness of the skin or mucous membranes due to capillary congestion (as in 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 projectiles
  • 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 

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]

Evidence must be preserved and secured from the time it is collected. It is vital to complete and maintain a chain of custody form. The form must contain information about the evidence collected and must remain with the evidence until it is released to law enforcement. The form must include the patient's identifying information with the date, time. The identity of each person who has had contact or possession of a piece of evidence from the time it is collected to the time it is released to law enforcement must be documented. Failure to provide this documentation will render evidence inadmissible in a court of law.

Important factors to follow when collecting evidence:[8][9]

Prevent contamination of the sample. 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. 

Preserve the original integrity of the sample. 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.

Maintain the individuality of the sample by labeling each specimen collected with the patient's identifying information such as the patient's date of birth, medical record number, date and time, and the signature or initials of the examiner.

Clinical Significance

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


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