The Trace Evidence Unit is one of the most diverse and unique of all disciplines in the Forensic Science Division (FSD) of the Michigan State Police (MSP). An examiner in this unit will see a wide range of evidence and must be proficient in several areas. The following types of evidence are some examples of those analyzed in Trace Evidence:
Paints (automotive and architectural)
Footwear and Tire Impressions
A Trace Evidence Analyst must possess a bachelor's degree in chemistry or other natural science with a strong background in microscopy, analytical instrumentation, and photography. An incoming analyst has a very extensive training period under a senior examiner. The incoming analyst may also be required to travel to other Michigan State Police Laboratories for training in certain disciplines. Each of the above disciplines must be studied, practiced, and mastered before the analyst begins performing their own casework.
A Trace Analyst may use a variety of instrumentation and visualization tools in their analysis of evidence including: Stereoscopic Microscopy, Polarized Light Microscopy (PLM), Fluorescence Microscopy, Scanning Electron Microscope/Energy Dispersive X-Ray (SEM/EDX), X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FT-IR), Gas Chromatography/Mass Spectrometry (GCMS), Pyrolysis Gas Chromatography (PGC), Ion Chromatography (IC), and Microspectrophotometry.
Fiber evidence is found in a variety of cases. When a struggle occurs between two people, fibers may be transferred from the suspect's clothes to the victim's clothes and vice versa. Carpet fibers from a home may adhere to a breaking and entering (B&E) suspect's shoes. A pedestrian struck by a vehicle may leave fibers from their clothing on the suspect's vehicle bumper or windshield. These are just a few of the types of crimes that may be solved by fiber analyses.
A questioned (Q) and a known (K) fiber can be compared using polarized light microscopy (PLM). The fiber type (i.e. Nylon, rayon, cotton, polyester, etc.), cross sectional shape, sign of elongation, and refractive index can be determined with PLM. Analytical instrumentation like FT-IR and Microspectrophotometry can be used to further identify and compare the Q and K fiber's chemical composition and color to determine if the two fibers could have originated
from the same source.
Paint can be transferred from one vehicle to another in an accident. An automotive paint chip left at the crime scene or on a hit-and-run victim's clothing can be used to determine the make and model of the vehicle it came from. Paint transferred from a window to a B&E suspect's tool can place that tool at the crime scene.
Paint is examined with microscopy and several analytical instruments to determine its layer sequence, binder type, and pigment content. If the Q and K paints are found to be similar in all these analyses, then they could have originated from the same source.
MSP Laboratories examine powders and exploded/unexploded devices to determine what type of explosive may have been used. After the MSP Bomb Squad renders a device safe, they submit a sample of the explosive (when the device is unexploded) or the debris (after an explosion occurs) to the Trace Unit.
These items are then analyzed with chemical spot tests and analytical instrumentation (FTIR, SEM/EDX, and IC) to determine their chemical make-up. This information will then be used to inform the submitting agency what type of explosive was used. These results can then be compared to any evidence found in the suspect's possession.
Fragments of glass can be compared to determine if they originated from the same source. When a pedestrian is struck by a vehicle, fragments of glass from the headlamp area or windshield may transfer onto the victim's hair and clothing. A criminal unlawfully entering a building or vehicle by breaking through glass will likely get fragments of glass on their clothing and on the tool used to break the glass.
In both of the above situations, glass particles (questioned glass) found by examining the clothing can be compared to particles collected from the crime scene (known glass) to determine if they have a common origin. Properties of the glass like tint, thickness, UV fluorescence, density, and refractive index, must all be similar for the questioned and known samples to have originated from the same source.
Headlamp and Bulb Filaments
Imagine you are carefully pulling out of your driveway late at night and your car is struck by a vehicle with its lights off. The police arrive and the person who hit you claims you pulled out in front of him. You explain to the police officer that the person who hit you did not have their lights on, so you did not see them. The other party replies that his lights were "definitely on". How is the officer to know who is right and who is wrong? The headlamp(s) from the vehicle in question can be submitted to the Trace Evidence Unit for examination. The filaments in the light bulbs are examined for oxidation, hot stretch, cold breaks, rainbowing, and fused glass particles. The analyst can then make the determination whether the headlamp(s) was on or off when the collision occurred.
Footwear and Tire Impressions
Footwear impressions and tire impressions are examined in a similar fashion to each other. Impressions can be three-dimensional when left in snow or soft soil, or they can be two-dimensional when a dirty, bloody, or wet origin impression is left on a surface. Footwear impressions can be as individual as a fingerprint. There may be thousands of other people that have the exact same shoe as you, yet as you wear your shoe, the tread wears down uniquely to your walking style. Also, accidental scratches, nicks, and cuts are left on the bottom of your shoe, which may be unique. Tires undergo the exact same changes making them unique as well.
Questioned impressions from crime scenes can be photographed, lifted, or cast with dental stone to compare to suspect shoes or tires. A comparison of tread designs or wear patterns can lead to a positive identification. An unknown footwear or tire impression can also be searched in laboratory databases to determine the possible make and model of shoe or tire that could have made that impression.
What is a fracture match? It is a comparison between two fractured, cut, broken, or torn objects to determine if they were at one time part of the same object. For example, if a car strikes a pedestrian and part of the grill breaks off and is left at the scene, it can be collected as evidence. Once the suspect car is found, the questioned piece of grill from the scene can be physically aligned to the car's grill to see if they were at one time one piece.
When an object is broken or torn, two unique edges can be formed. These edges can be compared visually and under a microscope to determine if their fractured edges re-align. If the edges fit together like a lock and key, they are said to form a fracture match to one another and the two objects were at
one time a single object.
When a suspicious fire occurs, a fire investigator investigates the scene. If they suspect an ignitable liquid may have been used, the investigator can collect areas where they believe the accelerant was used. These samples are placed in nylon bags or sterile metal cans, sealed air tight, and submitted to the Trace Evidence Unit for examination.
The samples are then documented and prepared for extraction. The samples are heated, causing any accelerant to go from the liquid phase to the gaseous phase and then adsorbed onto a strip of activated charcoal. The charcoal will absorb any accelerant molecules that may be present. The charcoal is then used for analysis. A solvent is used to extract the accelerant from the charcoal. The resulting solution is injected into a GC/MS to identify the type of accelerant used.
Sometimes the Trace Evidence Unit is referred to as the "Catch-all" Unit. There are many other different types of potential evidence or unknowns found at crime scenes. Acid/foil bottle bombs are submitted to determine what type of chemicals were used. Bank dyes from a suspect's clothing can be compared to bank dye from exploding dye packs to determine if they are similar. Lubricants and cosmetics (lipstick, mascara, nail polish, etc.) can be examined and compared along with feathers, safe insulation, plastic bags, tape, and the list goes on.
When a piece of evidence is brought to the laboratory and no other units are able to analyze it, the Trace Evidence Unit will often receive that
evidence and using a variety of appropriate laboratory techniques, identify or compare those items, providing valuable investigative information.
Questioned Document Examinations
Examinations are conducted on questioned documents in all types of criminal cases for local, state, and federal agencies. This includes the examination of writing, printing, ink, paper, impressions, typewriting, typewriters, checkwriters, photocopiers, alterations, obliterations, reconstructing torn, faded, charred, burned, or water soaked documents, to name a few. Laboratory reports are issued to submitting agencies, and expert testimony is given in various court proceedings. Some of the examination areas are:
Writing and Printing
Writing and printing is examined to attempt to identify or eliminate a writer. It is possible for writing to be identified or eliminated with known persons writing samples. Writing and printing is examined and compared with writing samples of known individuals in order to determine whether or not they wrote a particular document in question. Writing cannot be analyzed for any type of personality trait; this practice is called graphology and falls outside recognized forensic sciences.
Ink can be examined to determine if different inks were used to produce a particular document in question. Inks that have been obliterated or destroyed through fading, burning, water, overwriting, chemicals, or other means can often be recovered and made legible. Although the Michigan State Police Questioned Document Unit does not offer ink age determination, arrangements can be made to have this type of examination conducted at a federal laboratory.
Paper can be compared with known samples to determine if the document in question is similar to a known sample.Paper can sometimes be dated or traced to a particular source or manufacturer. Paper can also be reconstructed, such as matches reconstructed to their match books, shredded or torn documents, cut documents, etc. Paper that has been burned, water soaked, or faded can often be restored.
Typewritten documents can be identified with a particular typewriter. Typewriting can also be classified to determine what type of machine was used to produce the document. In addition, typewriter ribbons, correction ribbons, and correction materials can be examined to determine if these materials were used to produce the document in question.
Photocopiers, Printers, Mechanical Devices
Any mechanical items used to produce documents can be examined and compared with the document in question. The actual device (or known samples from the device) is submitted for examination to determine if the particular device was used to produce a document in question.
Unusual "Documents" or Document Cases
Some examples of unusual "documents" are: writing in blood, spray painted messages on buildings, writing, tattoos, stamps or other potentially identifying markings on human skin, matches found at the scene of a crime for comparison with a known matchbook.