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Trace Evidence Procedure Santa Ana Police Department 6101 Santa Ana PD Procedures Manual TRACE EVIDENCE 6101.1 PURPOSE This procedure establishes guidelines for the proper identification and collection of trace evidence. 6101.2 INTRODUCTION Trace evidence is defined as small evidentiary particles and includes, but is not limited to, hair, fibers, glass fragmentation, paint transfers / chips, gun shot residue, fire debris, botanical material, soil, and unknown chemical solids or liquids. Locard’s Exchange Principle states that whenever two objects come into contact a transfer of material will occur. The transfer may be primary (direct) or secondary (indirect) and usually involves trace evidence. Personnel responsible for the collection of trace evidence at any crime scene shall adhere to the following guidelines. Their actions or inactions should be based upon the particulars of each crime scene and firmly rooted in accepted forensic practices. 6101.3 PROCEDURE FOR LOCATING/IDENTIFYING TRACE EVIDENCE The following methods for detecting trace evidence at crime scenes are acceptable. No one method is correct for any given circumstance and it is recommended that more than one, if not all, methods be used to locate potential trace evidence at a scene. 1. Using direct light can be a very effective way of locating trace evidence. The brighter the light source, the more likely the forensic investigator will notice subtle differences in color and contrast of adhering surface particles. 2. Oblique lighting takes advantage of differences in the reflective qualities of particles versus the reflective qualities of the surface on which the particles reside. This method works well under low ambient light conditions. 3. Magnification is always advantageous. This method differentiates between particles with similar gross appearances and for making visible particles, which would otherwise go unnoticed. 4. Use of an Alternate Light Source (ALS) is often useful for visualizing many otherwise invisible evidentiary particles at scenes. It is important to note that different wavelengths used in combination with various filters each may reveal something new and previously unnoticed. The forensic investigator is encouraged to try all combinations of wavelength and filter. 6101.4 DOCUMENTING TRACE EVIDENCE As with any item of evidence, it is imperative that thorough documentation through accurate note taking, sketching, diagramming and/or photography (with and without scale) take place prior to collection. Because trace evidence is small by nature, overall, midrange and close-up photographs depicting where the item is relative to other items in the scene is imperative. Close-up photographs of trace Copyright Lexipol, LLC 2021/05/05, All Rights Reserved. TRACE EVIDENCE - 1 Published with permission by Santa Ana Police Department Santa Ana Police Department Santa Ana PD Procedures Manual TRACE EVIDENCE evidence should always fill the frame. Keep in mind that photographic filters may also become necessary to best document the evidence. Notes may include sketches and should be clear, concise and easily read by any viewer. Abbreviations should always be defined. Forensic Notes will become the foundation of your report and are susceptible to both peer review and later discovery. 6101.5 COLLECTING TRACE EVIDENCE In most instances, trace evidence should be collected prior to the collection of biological or fingerprint evidence, although there may be exceptions. Be aware of other forms of potential evidence that could be destroyed or altered because of the collection technique. The following techniques may be applied to the collection of trace evidence: 1. Hand Picking – Disposable or sanitized forceps, tweezers, and magnets, as well as gloved hands, can be used to remove some trace evidence, collecting the larger particles first. Magnification and a bright light sourceaid in this technique. Hand Picking is beneficial because, not only is it a one step process, but also it allows the forensic investigator the ability to document exactly where the particle(s) came from. Individually collected hairs and fibers may be placed on a clean “POST-IT” style paper or weigh paper for later packaging. 2. Tape Lifts - Using manufactured Tape Lifts or a roll of clear “inspected” sealed tape that is by definition free of debris, cut an approximate 20cm strip and apply the adhesive side of the tape to the questioned surface. Be sure not to overload the tape to the point that all adhesive is used. Apply the strip to an inspected clear plastic sheet protector, and repeat until the trace evidence has been sufficiently collected. Be careful with the edges of the tape so as to prevent accidental debris collection. Once complete, the tape roll should be placed back inside the now open heat seal bag for re-inspection. See below for inspection guidelines. (a) Each lift should be sufficiently labeled. Notes should include the name and date of who had previously inspected the tape, where the lift came from, date and time of collection, how the tape lift was labeled, case number, etc. This method is not to be used for wet or oily surfaces. (b) Tape lifting will successfully lift gunpowder particles; however the nitrocellulose in the gunpowder residue will slowly dissolve in the adhesive of the tape. Therefore, the case agent should be advised to contact the Orange County Crime Lab for expeditious processing of the tape. (c) Tape that has not been inspected prior to use shall not be used for trace evidence collection. Inspection consists of viewing the tape roll under the microscope, removing all foreign debris and heat-sealing the tape in a clear plastic bag. The individual responsible for the inspection must place their initials, along with the date and time of inspection, in permanent ink on the exterior of the sealed bag. This inspection must take place between each use of the tape roll. 3. Scraping – Using a sanitized metal scoopula or wooden tongue depressor, scrape the questioned item over a large piece of paper. The paper must be large enough to Copyright Lexipol, LLC 2021/05/05, All Rights Reserved. TRACE EVIDENCE - 2 Published with permission by Santa Ana Police Department Santa Ana Police Department Santa Ana PD Procedures Manual TRACE EVIDENCE collect any evidence falling from the item being scraped. This can be a time consuming processing. 4. Collection of the Entire Item – At times it may be more effective to collect and package an entire object for direct lab analysis. Examples of this may include, but are not limited to, paint transfers on a pry object, glass embedded in a baseball bat, clothing, vehicle floor mats, etc. Special attention should be paid as to how the item is packaged, preventing loss of any evidentiary particles through the packaging. If the item is, for example, clothing, the corners of the paper bag should be taped. 6101.6 PACKAGING TRACE EVIDENCE Trace evidence may be packaged in paper bindles or folds. It may also be placed in a coin-sized envelope so long as all seams are sealed to prevent evidence loss. The bindle, fold, or coin-sized envelope shall then be placed in a larger evidence envelope for booking. Glass vials or plastic specimen containers may be used for mineral, soil and other dry botanical materials. Please note that this packaging is not suitable for wet or moist samples. All packages must be sealed at the closure in such a way as to prevent access. Placing red evidence tape at the closure and including the collector’s name and date of collection is one way to accomplish this. Take care not to break, crinkle or damage hairs by folding them into the bindles. Firmly attached trace evidence (i.e. glass shards embedded in a collectable object) should be documented and packaged intact with the item. Pieces of clear, inspected tape may be placed around the trace evidence to ensure that they stay in place. Easily lost trace evidence or evidence which is impractical to transport shall be documented and collected at the scene. If there exists the possibility of a physical match, the entire item and possible source shall both be collected, however shall not share a common packaging. The item(s) shall be properly documented with photographs (with and without scale) and notes prior to collection. Unknown or questioned samples shall never share a common package with known standards. 6101.7 SPECIFIC CIRCUMSTANCE TRACE EVIDENCE - LACHRYMATORS (TEAR GAS/ OC/MACE) Lachrymators are chemicals that are mucous membrane/skin irritants and are defined by California Penal Code 12401. They are frequently encountered in officer involved shooting cases. Clothing suspected of containing lachrymator residue shall be sealed in an airtight container immediately upon collection (i.e. unused one (1) gallon paint can). 6101.8 SPECIFIC CIRCUMSTANCE TRACE EVIDENCE - ADHESIVE TAPES The adhesive side of tape can provide trace, fingerprint and DNA evidence. Evidentiary adhesive tape should be fastened so that it will remain stationary, inside a gun box with the adhesive side up. Refer to Forensic Services Latent Print/Chemical Processing Manual for further information reference the analysis involved with processing adhesive tape. Copyright Lexipol, LLC 2021/05/05, All Rights Reserved. TRACE EVIDENCE - 3 Published with permission by Santa Ana Police Department Santa Ana Police Department Santa Ana PD Procedures Manual TRACE EVIDENCE 6101.9 SPECIFIC CIRCUMSTANCE TRACE EVIDENCE - SOIL AND POLLEN Soil and pollen provide associative evidence. Put simply, soil and pollen collected from a crime scene can associate the suspect or victim to a particular geographical area. Similarly, soil found on a suspect or victim or his/her conveyance (i.e. vehicle, bicycle, plane, etc.) can associate them with a scene. Soil and pollen are class evidence and when an unknown or questioned sample is compared with a known or standard sample, the conclusion will be one of inclusion or exclusion and cannot be definitive.
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