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1. Trace evidence: 2. Types of trace evidence: 3. Forensic Science Errors/Mistruths

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Footprint cast from crime scene 5

6 is physical evidence found in small amounts at a crime scene. E xamples: hair, fiber, paint chips, body fluids, stains, powders, explosive residue, glass particles, vegetative matter, metal particles, and soil. It may also include more unusual types of evidence. Trace Evidence

 A torn piece of paper  Itching powder  Ashes  eyeshadow  A spider  Chewing gum  A match  Grease  Linoleum 8

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Physical property: not involving change in identity of a substance, such as: odor, color, boiling point, density, refractive index. Chemical property: determining how substance will change into another substance with different physical properties. 16

Bits of metal can be identified from their physical and chemical properties.  Solid particles: by microscopic examination, magnetism, malleability, density, color, solubility, reactivity  Dissolved metals: separation by chromatography with comparison of R f values to known metals, specific reactions and color tests 17

18 Solid metal particles found in a loaf of bread.  Were they in the flour from the manufacturer?  Or were they introduced by the plaintiff for personal gain?  Their identity answers these questions.

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20 Seasonal flooding caused crop failure and livestock sickness  The water was tested by chromatography  The separated metals had to be located with uv light  The spots were developed chemically and compared to standards

The metals were identified, but where did they come from?  A magnet manufacturer?  A maker of brass hardware?  A rechargeable battery company? 21

The metals were traced back to an abandoned mine 22

When investigators find substances at the scene of a crime and send them to the laboratory for identification, the forensic chemist uses several techniques or lab tests to identify them. One of these techniques is qualitative analysis.  A number of white powders that appear the same can be identified by their physical and chemical properties. 23

24 Microscopic Examination

25 Solubility pH: acidic? basic? Chemical reactions  Color  Precipitate formation  Evolution of gas

Paint: important in the case of hit and run accidents, where fragments of paint might have been transferred to a victim's clothes or to another vehicle. If a match can be made between paint chips and the missing flakes of paint using microscopy, then a suspect may be either eliminated or convicted 26

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 Kendall/Hunt Publishing Company 27

Sometimes the Trace Evidence Unit is referred to as the "Catch-all" Unit. There are many different types of evidence or unknowns found at crime scenes which are submitted to the Trace Unit to make a determination as to what it is or to make a comparison. 28

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In 1912, Emile Gourbin, a bank clerk in Lyons, France, who was suspected of strangling his girl friend, Marie Latelle. Gourbin was arrested although he had an air-tight alibi. Edmond Locard went to Gourbin ’ s cell removed scrapings from under his fingernails which contained tissue possibly from Marie ’ s neck, but this was not provable. Locard noticed that the tissue was coated with a pink dust, which he identified as rice starch. On the particles he found bismuth, magnesium stearate, zinc oxide, and a reddish iron oxide pigment called Venetian red. 32

Examination of face powder used by Marie revealed that a powder prepared for her by a Lyons druggist was similar in composition. In these days of mass- produced face powder, this evidence would have far less significance. However, in 1912, because of the special preparation, it led to the confession of Gourbin y/Geoforensics%20Case%20Histories.htm

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Thin layer chromatograph (TLC) can be used to separate the components of a lipstick. The chromatograms can then be compared for a match. 35

A bank robber was startled by an alarm just as the teller handed her the money. “She” grabbed it and in her haste to get away, ran smack dab into a glass door. Nevertheless, she recovered and got away. Subsequent examination of the door revealed a red lipstick imprint of the perpetrator’s mouth. Later police picked up a suspect, but needed evidence to link her to the robbery. 36

Of several suspects, one was identified by matching his lip print to that on the bank door. The lipstick used by the suspect could also have been compared to the residue on the door…. A "He" or a "She?“ 37

Six blond hairs 38

Maple seed pods 39

old death caseold death 40

Snowball's DNA "pawprint" 41

sticky case 42

... can you find it? 43

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