Trace Evidence and Alternate Light Source Notes
Trace Evidence and Alternate Light Source
Terminal Performance Objective
Process a crime scene using various Alternate Light Sources (ALS) and forensic collection equipment.
Properly identify, collect, package, and document trace evidence.
Discuss how to properly identify potential trace evidence.
Discuss alternate light sources and their uses.
Discuss proper setup and use of the UltraLite ALS.
Discuss proper methods for the collection and documentation of trace evidence.
Identifying Potential Trace Evidence
Trace evidence can be transferred from a victim to a suspect, or from a suspect to a victim.
Trace evidence often helps to establish the guilt or innocence of possible suspects.
Analysis of trace evidence is used in the investigation and prosecution of civil as well as criminal proceedings.
Trace evidence can be used to link crimes that are thought to be related to one another.
Special care must be taken in the collection of these items.
EPO #1: Properly identify potential trace evidence
Trace evidence is the general term used for the small, often overlooked pieces of evidence that are left at a scene.
Examples include:
Fibers
Hair
Soil
Wood
Gunshot residue
Pollen
These may be transferred between people, objects, or the environment during a crime.
Linking Suspects and Victims
Investigators can potentially link a suspect and a victim to a mutual location through trace evidence.
Example: A fiber sample obtained from a suspect’s person can be identified through scientific analysis as originating from a garment worn by the victim.
The analysis of the fiber evidence can help establish if the victim and suspect were in the same area.
Importance of Meticulous Effort
Identifying trace evidence is time-consuming and easily overlooked.
It requires meticulous effort.
Trace evidence is commonly searched for and collected early to avoid damage, contamination, and/or destruction.
Biological Materials
Biological evidence can be referred to as biological materials or substances such as hair, tissue, bones, teeth, blood, semen, or other bodily fluids.
Includes items containing biological material and used to corroborate and provide a means of proofing statements or claims in trials
Examples of Biological Trace Material
Blood and bloodstains
Semen and vaginal secretion stains
Saliva
Urine
Tissues and cells
Bones and organs
Fecal matter and fecal stains
Vomit
Stomach contents
Sweat
Hair as Trace Evidence
Hair is likely one of the most common types of trace evidence.
Hair is extremely variable among both individuals and racial populations.
Great care must be used in the use of hair as evidence.
Hair may, in some cases, rule out certain populations or help identify an unknown victim.
Cross-transfer of hair from a victim to a suspect or vice versa may substantially raise the probability that the victim and perpetrator were in contact.
Can never be used as a “smoking gun”. Only expressed in terms of probabilities of a match rather than absolute match.
Hair examinations can determine if a hair is animal or human.
If animal, the species and possibly breed of the animal can be determined.
Fibers as Trace Evidence
Fibers are everywhere.
Because they are so ubiquitous, they have a high chance of being transferred during a crime.
If recognized and collected properly, fibers may be able to link various individuals and places involved in a crime.
Fiber evidence is not just restricted to carpets and clothing.
Fiber examinations can determine if a fiber is natural or man-made.
Questioned fibers can be compared to fibers from a known source to determine if they are consistent with having originated from that source.
Questioned fibers can also be compared to other questioned fibers to determine if they are consistent with originating from the same source, though that source is not known.
Any object that contains fibers is useful for investigative purposes.
Some objects that have been tested in the past include wet suits, window screens, wigs, towels, and fishing lines, to name a few.
Determining the types of fibers found may also give an investigator some leads as to what objects were around at the time the crime took place.
The majority of the analyses performed for fibers are done so on a polarized light microscope.
This microscope aids the analyst in determining many optical properties of the fibers, which in turn helps the analyst identify the fiber type and compare those results to other fibers within the case.
Fabric examinations can determine if a questioned piece of fabric and a known piece of fabric are consistent in color, construction, and composition.
Torn pieces of fabric can be physically matched to a damaged garment.
Gunshot Residue (GSR)
GSR, also known as cartridge discharge residue (CDR), “gunfire residue” (GFR), or firearm discharge residue (FDR), consists of all of the particles that are expelled from the muzzle of a gun following the discharge of a bullet.
It is principally composed of burnt and unburnt particles from the explosive primer, the propellant (gunpowder), and vaporized lead.
The act of firing a bullet incites a very violent explosive reaction that is contained within the barrel of the gun, which can cause the bullet, the barrel, or the cartridge to become chipped.
Gunshot residue may also include metal fragments from the cartridge casing, the bullets jacket, as well as any other dirt or residue contained within the barrel that could have become dislodged.
Collection of gunshot residue (GSR) and the subsequent analytical identification of the primer components lead, barium, and antimony can be used to link an individual to the discharge of a firearm.
Paint as Trace Evidence
Motor vehicles, structures, tools, and other objects frequently have a protective or decorative coating applied either by the manufacturer or consumer that is generally described as paint.
Paint transfers can occur in many instances during the commission of a crime.
For example, when a vehicle collides with a pedestrian, paint can be transferred from the vehicle to the victim’s clothing.
When force is used to gain access to a building during a burglary, cross-transfer of paint can occur.
A painted tool may leave paint flakes or smears on a window frame. At the same time, paint from the window frame may transfer onto the tool.
The majority of paint cases submitted to the laboratory involve either automotive paint or architectural paint, but any type of paint or coating could be submitted for examination.
The purpose of forensic paint examination is either to compare paint from one source to that recovered at another or to determine a possible source of a recovered paint by searching a paint database.
Dried paint is usually a combination of organic and inorganic materials and can be comprised of many layers.
A forensic paint examiner will use a variety of tools to identify and compare paint samples submitted to the crime laboratory, including a stereomicroscope, polarized light microscope, and analytical instrumentation that can give the examiner distinct information about the paint’s characteristics and composition.
Paint examination can be a useful tool in a criminal investigation.
Glass as Trace Evidence
Broken/shattered glass can be discovered at an indoor or outdoor scene.
Exercise caution when dealing with glass; sharp edges can be hazardous to work with.
The broken edges can assist in identifying the method of entry as well as the direction of force applied.
Trace evidence from the tool used may remain on the glass and help identify the tool used to apply the force.
It is important to look for other surfaces that may contain trace fragments, such as the suspect’s/victim’s hair or clothing left behind from the incident.
Latent prints are still possible and can be lifted from the broken glass if proper technique and safety are maintained.
Fracture pattern analysis may be valuable.
Points of entry and exit of a projectile can be determined by analyzing the debris field caused by the impact of the projectile, i.e., a large portion of glass shards found inside the window seal of a structure would indicate the projectile originated from the exterior.
Soil as Trace Evidence
Soil is also considered biological evidence, and it contains identifiable components that can be used to match an origin (general/specific).
Therefore, do not remove foreign substances from evidentiary items unless necessary.
Soil can be discovered in a variety of locations, i.e., shoes, tires, undercarriage of vehicle, clothing, under fingernails, floor mats, etc.
It can be used to help corroborate/refute a statement and/or alibi.
Collect samples from known possible areas (5-30 feet away from the scene).
If relevant, take samples from the same depth as the suspected origin.
Botanical Materials
Forensic Botany can provide significant supporting evidence during criminal investigations.
Species identification of botanical trace evidence may provide links between crime scenes and individuals or help verify alibis.
Identification has been performed using morphological techniques, preventing small or damaged fragments from being identified at the species level.
Forensic Geologic Services
The FBI Laboratory is one of only a few crime laboratories that provide forensic geologic services.
The Mineralogy Group provides both laboratory analysis and field assistance for cases involving geologic evidence. This includes both naturally occurring and man-made geologic materials.
Materials examined typically include soil, glass, building materials, and gemstones.
Additionally, through an agreement with the U.S. Geological Survey (USGS) The Mineralogy Group can now supplement forensic soil examinations with pollen analysis.
Typical examinations include a comparison to assess a common origin, identification of an unknown material, and assessment of the geologic origin or geographic attribution of a material (provenance).
Searching for Trace Evidence
Searching for trace evidence can take patience and, in some cases, specialized equipment such as:
Magnification
Direct white light
Oblique lighting (angles)
Ultraviolet lighting
Alternate Light Sources (ALS, Krimesite Imager)
EPO #2: Alternate Light Sources (ALS)
An alternate light source is comprised of a powerful lamp containing the ultra-violet, visible, and infrared components of light.
It then filters down the light into individual color bands that enhance the visualization of evidence by light interaction techniques, including fluorescence, absorption, and oblique lighting.
Have been used to detect biological pieces of evidence, whereas this method is simple, presumptive, non-destructive test and applicable for detecting most types of biological evidence.
Over many decades, visible light sources were used during most searches of crime scenes.
Although some forensic investigators occasionally use ultraviolet to look for crime scene evidence, white light was the mainstay.
An ALS can be used to locate fingerprint evidence.
The initial search of the area, depending on the alleged crime that took place, could be conducted with the ALS.
Contrast is improved several times when ALS is used in conjunction with fluorescent powders, dye stains, and/or cyanoacrylate while canceling out all background colors.
Utilizing ALS techniques allows the latent print to be detected with much more sensitivity (10-100 times more!) than the conventional method of black powder dusting and lifting.
Alternate light sources can detect biological pieces of evidence due to their natural characteristics, such as light absorption (blood) or fluorescence effect (semen, saliva, and urine).
Oblique Lighting
Searching for hard-to-find evidence using a Flashlight at an oblique angle is particularly useful.
Lay the flashlight down on the floor, so the light Is broadcast across the floor.
You will see dust, dirt, and maybe footprints.
Oblique lighting uses a light source positioned at a low angle.
Oblique lighting is usually used to show detail by creating shadows on the surface of the evidence.
Oblique lighting is commonly used when photographing impressions, tool marks, and certain types of fingerprints.
An extremely low oblique angle of lighting can be used to photograph dusty footwear impressions and indented writing.
Photoluminescence
Bodily fluids will absorb light of a particular color and then emit light of a different color.
Using photoluminescence is easily achieved with a properly tuned ALS and camera barrier filter or goggles.
Ultraviolet Waves
Nano Meter (NM):
Nano stands for one billionth.
considered short-wave
3 types of ultraviolet waves:
Short: 100-280nm UVC
Medium: 280-320nm UVB
Long: 320-400nm UVA
All these are energy, but only 3 are considered light energy ultraviolet light, visible light, infrared light
Blood Detection with ALS
Blood has high absorption in a very broad region of light wavelength from 300-900nm, covering the entire light wavelength, including UV, visible, and IR light.
Hence, bloodstain will occur as a dark spot when it is exposed to any type of light.
Untreated, dry blood does not show a significant fluorescence effect.
Semen Detection with ALS
Dry semen has a strong photoluminescence.
The best fluorescence effect of semen stains was found at the wavelength of 420nm and 450 nm, observed with human eyes through orange goggles.
Saliva Detection with ALS
A dry saliva stain is virtually colorless and difficult To detect with the naked eye.
Exhibit a fluorescence effect in a lower-intensity compared to semen.
Detectable by the naked eye when exposed to UV light.
Would appear bluish-white, but this would not differentiate them from other stains.
Urine Detection with ALS
Hard to see because of the nature of Urine, where these stains will become diluted on fabric.
Best detected by human eyes under 415nm Excitation wavelength with yellow goggles.
Bruises and Wounds Detection with ALS
Forensic Light Sources may reveal bruises and patterned wound details that are invisible under normal white light illumination.
Details of a bruise on a victim, for instance, a bite mark or a shoe mark, can link a suspect to the victim.
Multiple wavelengths are necessary because different Colors penetrate to different depths within the skin.
Depending on the depth of the bruise or wound, you will need to vary the instrument’s wavelength.
Deep wounds may require infrared illumination to get enough skin penetration.
Ink Variations Detection with ALS for Questioned Documentation
Inks have different formulations, even within the same apparent, visible color type.
A tunable Forensic Light Source can be used to identify slight variations in ink type by viewing ink responses as the color of light is tuned through the visible and infrared regions.
Regardless of the skill of the forger, this exam would reveal that two different pens were used on the document.
EPO #3: Proper set up and use of UltraLite ALS
The UltraLite ALS size, weight, and ergonomic design make it the easiest and most comfortable to use the Alternate light system.
The LEDs on the Ultralite ALS do not have delicate filaments and are not jar sensitive.
Helps to reveal small bits of fiber, paint, hair, glass, crystals, and other "trace evidence", which can be physically difficult to find at a crime or accident scene, can be located using alternate light.
Items included in the Kit:
1 UltraLite One handle/head
1 Rechargeable battery pack
1 Battery charger
1 pair of amber glasses
1 pair of yellow glasses
1 pair of red glasses
Changing the battery only requires the user to press the release button to eject the battery and then snap it back into place.
Dead batteries can be charged in 3 hours.
90 minutes continuous use.
Ergonomically shaped with a trigger activation button, making it easy to hold and turn on/off with one hand.
Changing wavelengths requires the use of the thumb-activated push button to cycle through them.
COL
An UltraLite ALS system can help an investigator locate:
Small pieces of fiber
Small pieces of paint
Small pieces of glass
Other trace evidence
EPO #4: Collection/Documentation of Trace Evidence
When collecting or examining items, care must be taken to prevent contamination and loss of trace materials.
If a case involves disciplines other than trace evidence, the involved examiners should confer before any work is undertaken.
Unless circumstances dictate otherwise, the trace evidence should be collected and preserved prior to other examinations.
Eliminate contact between items and personnel before the appropriate trace evidence has collected.
General Principles and Practices to Avoid Evidence Contamination and Loss
Applicable to both lab and non-lab settings, include:
Appropriate protective apparel, such as laboratory coats and disposable gloves, must be worn to prevent contamination from the clothing of the examiner.
The apparel must be changed as necessary to avoid contamination or transfer between evidentiary items, locations, and personnel.
Equipment and work surfaces used during collection and examination must be cleaned in an appropriate manner before processing begins and as often as necessary during processing to prevent contamination.
Adhesive lift materials must be maintained in a manner to avoid contamination.
Caution should be used to prevent tape edges from contacting any uncleaned surfaces.
All biological evidence is subject to deterioration.
Items being collected for trace evidence examination must be handled as little as possible to minimize loss of the trace evidence and to limit exposure of the items to contaminants.
Collect, package, and seal items individually in appropriate packaging.
Keep items in a secure, sealed package until the item is processed in a controlled environment.
Adhesive-Coated Transparent Tapes for Trace Evidence Recovery
Adhesive-coated Transparent tapes have long been used as the tool of choice when recovering trace evidence from a variety of sources.
These tapes have a number of key advantages:
Their ability to readily isolate evidentially valuable materials from the substrate on which they are found
The fact that these materials can be easily secured by adhering the tape to a suitable backing, such as an acetate sheet
The transparency of these tapes also means that low-power microscopy can be used to search for trace items that may be adhered to them
When you collect the trace evidence, ensure you are collecting sufficient amounts.
Do not package exemplar, standard/reference, or control samples with the evidence.
Package them separately.
Standard, reference, and control samples should be collected for laboratory comparison, examination, or elimination purposes.
Collect enough for multiple analyses.
Collect the entire holder of evidence if/when possible/feasible. If not, then individual soft collection tools should be used.
If you need to use tweezers or forceps to collect trace evidence, use only sufficient pinching force to collect the item to prevent altering or damaging the evidence.
Tape Lift Method
Take a piece of tape that is long enough to cover the location of potential evidence and tear it from the roll.
Lay the tape, sticky side down, on the location where the evidence is being collected from.
Press on the tape to ensure that you are getting good contact between the sticky portion of the tape and the potential trace evidence.
Once you believe that you have good contact, pull the tape away from the location you are collecting the trace evidence and secure it to acetate.
If you do not have acetate at your station, then you could use a Zip-Lock baggie.
Using Zip-Lock Baggies for Trace Evidence Collection
Take a Zip-Lock baggie. The size will depend on the evidence collected and open the end with the zipper.
Tear down the sides of the baggie (avoid cutting to prevent the introduction of any foreign substance) so that three ends of the Zip Lock baggie are now opened.
Leave the manufacturer’s folded end of the Zip Lock baggie intact.
Open the baggie so that what was the inside of the closed bag is now exposed and face up.
Put any unused portion of the roll of tape into a clean plastic bag and seal the bag.
Packaging Guidelines
Trace evidence should not be placed directly inside manila envelopes of any size or paper bags.
Because trace evidence is so small, it should be placed into a leakproof container first and then into a paper type of container like an envelope.
Collecting Wet Evidence
There could be a situation where Wet collecting evidence is necessary.
First, determine if the liquid is relevant to the case.
Place the item with the liquid in it in a secured room and allow it to dry.
Prepare an area for drying by having a clean table.
Place a clean piece of paper on the table/floor. Size depends on the size of the item being dried.
Allow the item to dry naturally, do not expose the item to heat or significant drafts like a blow-drier.
Never leave the item in the sunlight.
Collecting Control or Comparison Samples
A control sample is one that the collector knows does not appear to have evidence present.
It represents the matrix material on which the evidence rests.
A comparison sample, on the other hand, may have evidence present without the collector’s knowledge.
It represents the matrix material on which the evidence rests or is made of the same matrix material as the evidence.
These items would be compared to the evidentiary samples.
The collection and labeling of these samples are the same as collection of evidence.
COL
When necessary to collect a “wet” evidence sample, the investigator should: place the evidence in a secure room to allow it to dry.
ALS and Trace Evidence Summary
Discuss alternate light sources and their uses.
Discuss how to properly identify potential trace evidence.
Discuss proper methods for the collection and documentation of trace evidence.
Discuss proper setup and use of the Ultralite ALS.