14.6: Biological Evidence from Victim and Suspects

Buccal Swabs

Buccal cells are located on the inner cheeks in the mouth and can be collected for DNA typing. Buccal swabs are usually used in place of obtaining blood.

• Only one sterile swab is needed for a mouth.
• Swab the inside of both cheeks by scrubbing the cheek walls on both sides with a sterile cotton swab.
• Place a shield over the applicator and return it to the sterile packaging. Seal the packaging and process it into evidence as normal. If the specimen is wet, it is best to place it in a refrigerated evidence locker. If the specimen is dry, it is acceptable to store it in temperature controlled dry storage.

Fingernail scrapings

Fingernail scrapings may contain trace evidence including blood, tissue, hairs, fibers or other foreign material that may have collected under the nails of the suspect or victim during a struggle or violent interaction. Moisten a sterile cotton swab in the manner described above and vigorously scrub under each nail to the nail bed. Use a separate swab for each finger and process the swabs individually. It is best to use an applicator shield to cover the cotton tip. Place a shield over the applicator and return it to the sterile packaging. Seal the packaging and process it into evidence as normal. If the specimen is wet, it is best to place it in a refrigerated evidence locker. If the specimen is dry, it is acceptable to store it in temperature controlled dry storage.

Bite marks

Bite mark impressions may be found on victims of an assault and can be compared with the teeth of the suspect. Photograph the bite marks with and without a scale and color chart. When using a scale, it is preferable to use a small L-shaped ruler, such as an ABFO #2 ruler, that is designed for bite marks. Also document the bite mark, including measurements. Slightly moisten a sterile cotton swab or sterile gauze pad with sterile water and rub around the bite mark area. Swab a second time around the area using a dry swab. Place the swab bag in its original sterile packaging and process it into evidence after allowing it to air dry in an area free of contamination.

Fired and unfired cartridge casings

Advancements in DNA extraction have made it possible, in certain circumstances, to acquire a genetic profile from a fired cartridge casing. It had long thought that the conductive properties of the metallic cartridge and the super heating that occurs with propellant discharge would evaporate the bodily fluids that contain DNA. However, in recent years various techniques, such as the soak and sonicate methods, have been successful in DNA extractions. Therefore, it is essential that the casings are properly collected at the scene with great care in reducing cross-contamination or sample degradation. To do this, your author has implemented strict guidelines at his agency that everyone must follow when collecting fired and unfired cartridge casings. Gone are the days of picking up fired cartridge casings with bare hands and tossing them in a plastic baggie. Gone are also the days of picking up the casings with gloved fingers. Today, every fired cartridge casing is picked up using a sterile tweezer and placed into an evidence box, the interior of which has been subjected to a three-minute short-wave ultra-violet bath. Each box should contain only one item of evidence. The technician is still required to wear gloves, and it is mandatory that they wear an N-95 mask. Your author is especially careful with bullets that are recovered from the crime scene. The object is to keep the bullets from rolling around within the box. Your author finds it best to use 2”x2” sterile gauze pads, wrapping the evidence item in the gauze pad, replacing it in the sterile envelope from which the pad was removed, folding it in a manner to keep the item from falling out (perhaps even a small piece of tape to secure the open end of the envelope), and placing it within the jewelry box.

Discussions should be had with investigators regarding subsequent cartridge casing analysis. Submission of fired cartridge casings to Integrated Ballistic Identification System, or IBIS, would preclude any additional forensic examination as the cases are thoroughly cleaned before imaging. The history of casings from cold-case investigations must be either known or deduced prior to submission to soak and sonicate laboratories, since the process is expensive and laborious.

Figure \(\PageIndex{1}\): Jewelry boxes used for evidence collection

Observations

Before handling an item of evidence, consider how a person would hold the item and avoid grasping it in the same place. Inspect these areas for human biological evidence and consider collecting a specimen swab as soon as possible. Consider your options before using any forensic process that will destroy, alter, or contaminate potential DNA evidence. Make every effort possible not to contribute your own DNA to the crime scene or upon items of evidence found within that crime scene. Never discard your used latex gloves into the crime scene and prevent others from doing the same.