Trace evidence can be found at crime scenes. It can be anything from strands of hair or skin cells to tool marks and physical (fracture) matches. Trace evidence can be used to identify a victim or suspect or determine how a crime was committed.

Hairs & Fibers

•         Hairs and fibers may be transferred from the suspect or the suspect’s clothes to the victims’ and vice versa.

•         A pedestrian struck by a vehicle may leave hairs and fibers on the suspect’s vehicle bumper or windshield.

•         Carpet fibers can attach to a suspect’s shoes.

•         Hair can usually be found on the floor near the weapon or point of impact between suspect and victim.

•         Hair with roots may provide individual DNA evidence. 

•         Hair also has characteristics.  There are 14 different elements that can be identified in a hair sample.    

•         Fibers are usually collected from clothing, carpeting, furniture, beds, and blankets. 

•         There are over a thousand known fibers, and several thousand known dye formulas.

Paint

•         Paint can be transferred from one vehicle to another in an accident.

•         A paint chip left at the crime scene can be used to determine the make and model of the vehicle it came from. Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles.  

•         Paint transferred from a window to a suspect’s tool in a break and entry can place that tool at the crime scene.

•         Paint is examined with microscopy and several analytic instruments to determine its layer sequence, binder type, and pigment content.

•         There are forty thousand different types of paint classified in a database available to police. 

Explosives

•         Powders and exploded/unexploded devices can be examined to determine what type of explosive may have been used.

•         After the Bomb Squad makes sure a device is safe, they submit a sample of the explosive or the debris to the Trace Unit.

•         These items are then analyzed with chemical spot tests and analytical instrumentation to determine their chemical make-up.

•         This will identify which type of explosive was used.

•         These results can then be compared to any evidence found in the suspect’s possession.

Glass

•         In car accidents, fragments of glass can be embedded in a victims’ hair or clothing.

•         In break and entries, suspects often get glass fragments on their clothing.

•         Glass particles can be compared to particles collected from the crime scene to determine if they have a common origin.

•         Glass tint, thickness, UV fluorescence, density, and refractive index can all be compared.

•         If enough glass is present to reconstruct a pane, often the direction of the impact or sequence of impacts may be determined.

Dust & Dirt

•         Can reveal where a person has been, where they live, where they work, and if they have pets.

•         Alibi soil samples are taken in many criminal investigations.

•         Most soil samples are from the top surface of the soil, and involve taking little more than a tablespoon.

•         Pollen can reveal where a person has been (outside).

Firearms

•         Includes ammunition, components and residue.

•         Characteristics are examined to fins a match.

•         Bullets are never removed from their holes. The whole surrounding surface is cut out. 

•         Bullets are usually never marked. 

•         Gunshot residue from the hand or face needs to be done within six hours, and a lab can compare it with target residue.

Fluids

•         Semen, saliva or sweat can usually be found in spatters, drops or stains.

•         It can be fresh, coagulated or in dried form.

•         Each form has its own particular method of collection and preservation. 

•         Bodily fluids, such as vomit, can be found at scenes involving alcohol, drugs, and poisons.

•         Cigarette butts may contain dried saliva

•         Semen containing sperm is particularly valuable for DNA analysis

•         Biological evidence must be transported to the lab quickly.

Blood

•         There are 150 known proteins, 250 known enzymes, and many more antigens in blood.

•         Investigators can often estimate the time a crime occurred from how dry the blood is.

•         The shape of blood at the scene (pool, drops, stains, or splashes) can provides clues as to what happened. 

•         Recording the location and description of bloodstains is usually the most detailed part of crime scene photography, sketching, and note-taking.

•         Blood evidence is frequently used to eliminate a pool of suspects.  

Bite Marks

•         Each of the thirty-two teeth in humans is unique due to age and wear.

•         Bites can tell how quickly the offender subdued the victim. 

•         Bites can often be matched to dental records.

Headlamp Filaments

•         In motor vehicle accidents, the officer can examine the headlights from a car in order to determine if the headlights were on at the time of the collision.

•         The filaments in the light bulbs are examined for oxidation, hot stretch, cold breaks, rain bowing, and fused glass particles.

Shoeprints

•         Footprints and footwear impressions and tire impressions are examined in the same fashion.

•         Impressions can be three-dimensional when left in snow or soft soil, or they can be two-dimensional when a dirty, bloody, or other impression is left on a hard surface.

•         Footwear impressions can lead to identification of a suspect because of the treads on the shoes that are worn down to each persons walking style. There may also be accidental scratches, nicks and cuts are left on the bottom of your shoe.

•         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.

Physical (Fracture) Matches

•         Comparison between two cut, broken, or torn objects to determine if they were part of the same object.

•         When an object breaks, tape is torn, or something is cut, two unique edges are formed. These edges can be compared by the naked eye, and under high magnification to see if they fit together like puzzle pieces.

•         If the edges fit together they are said to physically match one another. It can then be said that the two objects were at one time a single object.

Arson Debris

•         Extractions and identifications are made using the gas chromatograph or the gas chromatograph/mass spectrometer.

•         Analysis is typically for the presence or absence of petroleum products although other non-petroleum based accelerants may be identified.

•         The presence of certain products can indicate that arson was involved.

Tool Marks

•         When a tool is made and used, tiny nicks and chips begin to form.

•         These nicks and chips characterize its blade and edges and pick up traces of substances it came in contact with.

•         Tool marks can be found at break and enters, robberies and other crime scenes where tools where used.

Wounds

•         Wounds can often be matched to weapons, tool marks on the weapon, or at least the weapon's size, shape, and length. 

•         Wound pattern analysis is a special technique that often provides clues. 

Questioned Documents

•         Everyone has a unique style of handwriting.

•         Most computers and printers also have a unique printing style.

•         Document examiners can establish similarities in handwriting, and computer forensics specialists can often determine the make printer used to type a document.

Miscellaneous Unknowns

•         There are many different types of evidence or unknowns found at crime scenes which are submitted to the Trace Unit.

•         The Trace Unit can determine what the items are or make a comparison.

•         They can determine what types of chemicals were used or determine a type of dye from a suspect’s clothing.

•         Lubricants and cosmetics can also be examined and compared.

•         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 the evidence and attempt to identify it through the use of numerous microscopic and chemical analyses.