Trace Evidence Hermitage Technical Center Criminal Justice Trace

Trace Evidence Hermitage Technical Center Criminal Justice

Trace Evidence w Definition - Trace evidence is evidence which must be examined, and attested to, by laboratory examiners to be admissible in court. HTC Criminal Justice

Jewelers’ Marks Soil Dust/Dirt Pollen Paint Serial Numbers Tool Marks Trace Evidence Hair & Fibers Fingernail Scrapings Firearms Bitemarks Blood. Stains Shoe &Tire Impressions Other Body Fluids HTC Criminal Justice Glass

Trace Evidence w GLASS -- Small pieces of broken glass (from doors, windows, or decorations) are frequently found on clothing and footwear. w It is also sometimes found on the weapon, tools, and skin. HTC Criminal Justice

Trace Evidence w PAINT -- Small chips of paint (from doors, walls, or furniture) are often found on weapons, pry bars, blunt objects, clothing, shoes. HTC Criminal Justice

Trace Evidence w There are forty thousand different types of paint classified in a database available to police. HTC Criminal Justice

Trace Evidence w Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles. HTC Criminal Justice

Trace Evidence w DUST/DIRT/SOIL -- This kind of trace evidence reveals: • • where a person has been where they live where they work whether they have pets HTC Criminal Justice

Trace Evidence w Most soil samples are from the top surface of the soil, and involve taking little more than a tablespoon. HTC Criminal Justice

Trace Evidence w POLLEN is a subtype of dust/dirt that reveals where a person has been outdoors. HTC Criminal Justice

Trace Evidence w FIREARMS -- This kind of evidence involves • Ammunition • Components • Residue w It typically consists of a whole host of family characteristics. HTC Criminal Justice

Trace Evidence w Bullets are never removed from their holes. w The whole surrounding surface is cut out. w Bullets are usually never marked. HTC Criminal Justice

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Trace Evidence w Gunshot residue from the hand or face needs to be done within six hours w A lab can compare it with target residue. HTC Criminal Justice

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Note the basic features of cartridges used in guns. The primer, when struck by the firing pin, ignites the powder. It is the residue left by the primer that is characteristic for a fired round, because it leaves traces of lead, antimony, and barium. HTC Criminal Justice

Trace Evidence w BALLISTICS - The science of ballistics is sometimes used for crime reconstruction. w It can confirm a statement or prove it false. HTC Criminal Justice

Trace Evidence w The shape of blood at the scene provides clues as to what happened • • pool drop stains splashes HTC Criminal Justice

Trace Evidence w At the scene, investigators often estimate the time a crime occurred from how dry the blood is. HTC Criminal Justice

Trace Evidence w Recording the location and description of bloodstains is usually the most detailed part of crime scene photography, sketching, and note-taking. HTC Criminal Justice

Trace Evidence w. A specialized technique known as bloodstain pattern analysis is one of the most common methods of reconstruction. HTC Criminal Justice

Trace Evidence w SHOEPRINTS -- Most people's shoeprints show individual signs of wear. w They are fairly unique given gait and walk. HTC Criminal Justice

Trace Evidence w Shoe impressions, like tire impressions, often contain contaminates or traces of evidence on them. HTC Criminal Justice

Trace Evidence w Only after it is certain that all residual trace evidence is cleared from the impression area is a plaster cast mold taken. HTC Criminal Justice

Trace Evidence w TOOL MARKS -- When a tool is made and used, it acquires tiny nicks and chips that characterize its blade and edges as well as picks up traces of substances it came in HTC Criminal Justice

Trace Evidence w Tool marks are most commonly found at burglaries on windowsills, window frames, door frames, cash register drawers, file cabinets, and any locked piece of furniture. HTC Criminal Justice

Trace Evidence w WOUNDS -- can often be matched to weapons, tool marks on the weapon, or at least the weapon's size, shape, and length. HTC Criminal Justice

Trace Evidence w. A specialized technique known as wound pattern analysis often provides behavioral clues. HTC Criminal Justice

Head Wound w The upper diagram illustrates the basic differences between the skin appearance of a contact, close (intermediate), and distant (indeterminant) range gunshot wound. The appearance of the wounding characteristics in the skull is shown in the lower diagram in which there is bevelling of the skull outward away from the direction of origin of the bullet. HTC Criminal Justice

Trace Evidence w Usually collected by investigators at the crime scene w Delivered or shipped to forensic laboratory to be examined and tested by specialists. HTC Criminal Justice

Trace Evidence w Lab examiners determine if the trace materials have evidence value for the case. Douglas Deedrick, Unit Chief Trace Evidence Lab, FBI HTC Criminal Justice

Trace Evidence w Lab examiners furnish information back to the investigators to use as leads. w The admissibility or the evidence in court depends on the examiner’s expert testimony. HTC Criminal Justice

Trace Evidence The usefulness of w Recognize the evidence depends on the w Collect investigator’s w Preserve ability to: HTC Criminal Justice

Trace Evidence w Can be as obvious as bloodstains w Can be as inconspicuous as dust particles HTC Criminal Justice

Trace Evidence w It is often: • Overlooked • Mishandled • Discarded as useless HTC Criminal Justice

Trace Evidence w May be left at a crime scene by the offender w May be carried away by the offender or investigators w May be destroyed by 1 st on scene HTC Criminal Justice

Trace Evidence w Suspect may leave • Tool marks • Bloodstains • Hairs and fibers • Soil • Similar traces - can you name any? HTC Criminal Justice

Trace Evidence Remember the Locard Exchange Theory? HTC Criminal Justice

Trace Evidence What happens to your evidence if you return the perpetrator to the scene before trace evidence is collected? HTC Criminal Justice

Trace Evidence w Make sure collected trace evidence is: • Not mixed with trace from other parts of the crime scene • Packaged separately • Properly preserved - avoid contamination HTC Criminal Justice

Hair and Fibers w Are valuable as evidence w Are seldom conclusive evidence w Used in conjunction with other details, they have proven to be important and essential. HTC Criminal Justice

Hair and Fibers w Helps to establish the scope of the crime scene w Helps place a perpetrator at the scene w Connects a suspect with a weapon. HTC Criminal Justice

Hair and Fibers w Supports or disproves witness statements w Connects crime scene areas • Abduction • Vehicle used • Dump site HTC Criminal Justice

Hair and Fibers w The origin and texture of hairs and fibers found at a crime scene or on the body, clothing, or headgear of a suspect or a victim may be highly important as evidence. HTC Criminal Justice

Hair and Fibers w Most often collected at • Homicide scenes • On body of deceased • On body and clothing of suspect of rapes and homicides. • On body of rape victim HTC Criminal Justice

Hair and Fibers w Transfer of hair and fibers often take place during any physical contact between the suspect and the victim w This is especially true in incidents of violent crime. HTC Criminal Justice

Hair w Hair is chemically stable especially when compared to other physiological materials such as blood, semen, or any other body fluid. HTC Criminal Justice

Hair w Because hair is strongly resistant from decomposition, its property makes hair a nearly ideal type of physical evidence. HTC Criminal Justice

Hair w. A strand of hair has three layers • Cuticle • Cortex • Medulla HTC Criminal Justice

Hair The cuticle is the outmost covering, and consists of hard overlapping scales that point toward tips end. w The cortex contains pigment granules that give hair its color. w The medulla is a hollow tube within the hair, which may be present or absent. Depending on the hair, this hollow tube is continuous, or fragmented. w HTC Criminal Justice

Hair w Examiner compares: • • • Color Coarseness Granule distribution Hair diameter Presence or absence of a HTC Criminal Justice

Hair w Because different hairs on the same person can show many variations, the larger the sample for analysis, the better. w An average sample ranges from 24 to 50 pieces. HTC Criminal Justice

Hair w Hair analysis can indicate whether the source is human or animal, and also whether the source is a member of a particular race. HTC Criminal Justice

Hair w Analysis can determine • If the hair has been dyed • If the hair was cut in a certain way • It it was pulled out • Where on the body it came from. HTC Criminal Justice

Hair w In some cases, evidence of poisoning shows up in the hair. w The hair shaft with a follicle can also offer genetic determinations, such as blood type or DNA. HTC Criminal Justice

Hair w w Characteristi cs of Caucasian Hair w w w Straight to wavy Evenly distributed pigment granules Fragmented medulla or absence of medulla cross section oval round fine to coarse pigment HTC Criminal Justice

Hair Dense pigment distributed evenly w Cross section round w Hair shaft coarse and straight w Presence of continuous medulla w Characteristi cs of Asian Hair HTC Criminal Justice

Hair Characteristi cs of African American Hair Curly w heavy pigment distributed unevenly w variations in diameter w fragmented medullae or absent of medullae w HTC Criminal Justice

Hair The characteristics of hair varies from species to species and from animal to animal within a species. HTC Criminal Justice

Fiber w Fiber is just as valuable as hair in crime scene investigation w Success in solving the crime often hinges on the ability to narrow the sources for the type of fiber found. HTC Criminal Justice

Fiber w The problem with fiber evidence is that fibers are not unique. w Like hair, they cannot pinpoint an offender in any definitive manner. HTC Criminal Justice

Fiber w For fibers to be valuable as evidence, there must be other factors involved, such as: • evidence that the fibers can corroborate, or • something unique to the fibers that set them apart. HTC Criminal Justice

Fiber w Fibers are gathered at a crime scene with • Tweezers • Tape • Trace vacuum HTC Criminal Justice

Fiber w Fibers • • • generally come from clothing drapery wigs carpeting furniture blankets HTC Criminal Justice

Fiber w For analysis, fibers are first determined to be • Natural • Manufactured • A mix of both HTC Criminal Justice

Fiber w Natural fibers come from • Plants • Cotton • Hemp • Animals • Wool • Angora HTC Criminal Justice

Fiber w Manufactured fibers are synthetics made from long chains of molecules called polymers. Some are: • Rayon • Acetate • Polyester HTC Criminal Justice

Fiber w To determine the shape and color of fibers from manufactured fabrics, a microscopic examination is made. HTC Criminal Justice

Fiber w Generally, the analyst gets only a limited number of fibers to work with—sometimes only one. HTC Criminal Justice

Fiber w Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home. HTC Criminal Justice

Fiber w The fibers are laid side by side for visual inspection through a microscope. HTC Criminal Justice

Fiber w The first step in fiber analysis is to compare color and diameter. w Dyes can also be further analyzed with chromatography. HTC Criminal Justice

Fibers w The analyst looks for • Lengthwise striations • Pits on a fiber's surface • Unusual shapes HTC Criminal Justice

Fiber w Fiber • • • analyst compares Shape Dye content Size Chemical composition Microscopic appearances HTC Criminal Justice

Fiber w This is still about class evidence. HTC Criminal Justice

Fiber w Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source. HTC Criminal Justice

Fiber w There is no fiber database that provides a probability of origin HTC Criminal Justice

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