CHAPTER 9: TRACE EVIDENCE
1. ____________________________________________________________________________________
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2. ____________________________________________________________________________________
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3. Common examples would be:
Unusual Types of Trace Evidence
1.
2.
3.
4.
5.
6.
7.
Physical and Chemical Properties
1. Physical property: A characteristic that does not involve a change in the
identity of a substance, such as:
2. Chemical property: A characteristic that determines how a substance
will change into another substance with different physical properties
Metal Analysis
Bits of metal can be identified from their physical and chemical
properties.
1. Solid particles—__________________________________________________________
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2. Dissolved metals—_______________________________________________________
______________________________________________________________________________
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Product Liability
Solid metal particles are found in a loaf of bread.
1. Were they in the flour from the manufacturer?
2. Or were they introduced by the plaintiff for personal gain?
3. Their identity answers these questions.
Analysis of Metal Particles: A Qualitative Analysis Approach
Testing for Metals
1) This metal is nonmagnetic, floats in bromoform and has a strong reaction
(bubbles) when tested with NaOH. ___________________________________________
2) This metal is nonmagnetic & sinks in bromoform. When tested with
HNO3 there was no reaction. When tested with HCL there was no
reaction. _______________________________________________
3) This metal is magnetic & slowly bubble when HNO3 is added and turns
green. __________________________________________________
4) This metal is nonmagnetic & sinks in bromoform. When HNO3 was
added, it turned blue. _______________________________________
Chromatography
1. ____________________________________________________________________________________
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2. The affinity of the unknown substance in each phase determines the
degree of separation.
3. This affinity may be related to:
1.
2.
3.
4. Stationary phase: ______________________________________________________________
____________________________________________________________________________________
5. Mobile phase: __________________________________________________________________
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Environmental Contamination
1. Seasonal flooding caused crop failure and livestock sickness.
2. The water was tested using chromatography.
3. The separated metals had to be located on the chromatogram with UV
light.
4. The spots were developed chemically and compared to standards to
determine the identity of the metals.
Environmental Pollution
The metals were identified, but where did they come from?
1. A magnet manufacturer?
2. A maker of brass hardware?
3. A rechargeable battery company?
Summary Questions:
1. A piece of metal is placed in a beaker bromoform (density of 2.89 g/cc). If the density of the metal
is less than that of bromoform, what will the metal do? Of the metals you tested, identify the
possibilities. Is density a physical of chemical property of aluminum?
2. Which of the common metals are magnetic?
3. What are some physical properties of a malleable metal?
4. What is meant by a confirmatory test? What is the confirmatory test for the detection of Al+3 ?
5. What metal contaminants were found in Mr. Calamimine’s water sample? Where did they come
from? What are the major components of stainless steel? Of Bronze? Of Pewter?
6. When you use paper chromatography for the metal analysis, what is the mobile phase? What is the
stationary phase?
7. What is chromatography? Could you use the same method in the Calamine case that you used in
the metal contamination case?
8. Why is pencil and not pen used to mark the chromatography strips?
9. How could Mr. Calamine clear his farmland of the current pollution?
Trace Evidence: Qualitative Analysis of Powders
1. 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.
2. One of these techniques is qualitative analysis.
3. For example: A number of white powders that appear the same can be
identified by their physical and chemical properties.
Qualitative Analysis
• Microscopic Examination
Check for:
1.
2.
3. Chemical reactions
Flame Colors
1. Many metal salts show a distinct color when heated.
Arsenic –
Barium –
Boron –
Calcium –
Copper –
Iron –
Magnesium –
Potassium –
Sodium –
Strontium –
Zinc –
2. Sometimes this property can be used in an analysis.
Summary Questions
1. In the qualitative analysis of white powders, what is meant by solubility? What factors may affect
the apparent solubility of the first ten samples? Is solubility a physical or chemical property?
2. In the analysis in question 1, what indicates that a chemical reaction has taken place?
3. Identify the white powder that dissolves in water, is colorless in phenophthalein, does not
produce a precipitate in NaOH, does not react with vinegar, insoluble in alcohol, and dissolves
quickly in hot water.
4. Identify the white powder that does not dissolve in water and turns deep blue in the presence of
iodine.
5. What is Rf and how is it calculated?
6. What causes metal salts to show colors in a flame?
7. Why can’t copper wire, rather than expensive platinum, be used for flame tests?
A Historical Crime
1. In 1912, Emile Gourbin was a bank clerk in Lyons, France. He came under suspicion of strangling
his girlfriend, Marie Latelle. Gourbin was arrested but had what appeared to be an airtight alibi.
2. Edmond Locard went to Gourbin’s cell and removed scrapings from under his fingernails.
3. The scrapings contained tissue that possibly came from Marie’s neck, but this was not provable.
4. 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.
5. Examination of the face powder used by Marie revealed that a powder prepared for her by a Lyons
druggist was similar in composition.
6. 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.
A More Recent Crime
1. A bank robber was startled by an alarm just as the teller handed her the money.
2. She grabbed it and, in her haste to get away, ran smack-dab into a glass door. Nevertheless, she
recovered and got away.
3. Subsequent examination of the door revealed a red lipstick imprint of the perpetrator’s mouth.
4. Police later picked up a suspect, but needed evidence to link her to the robbery.
5. Are lip prints unique enough to tie the suspect to the crime?
Lip Prints
1.
2. There are several general patterns:
Chromatography of Lipsticks
1. The lipstick used by the suspect could also have been compared to the
residue on the door.
2. ________________________________________________ can be used to separate the
components of a lipstick.
3. The chromatograms can then be compared for a possible match.
Paint
1.
2. The layers of different paints in a cross section may be unique.
3. House paint can be found on a jimmy or other type of tool used in the
forced entry for the purpose of burglary, assault or rape.
4. Art Forgery –
Vehicular Hit-and-run Cases
1.
2.
3. New Cars have 4 coats of paint:
4. Examining a cross section of paint chips at 10-40X reveals these layers
5. Sideswipe – smear of the top layer of the car’s paint may be transferred to
the struck object.
6. The make, model, & year of the vehicle can be identified from a paint chip.
The VIN provides information about the vehicle including the color.
Summary Questions:
1. What single instrument is the forensic scientists best friend?
2. Why do more layers of paint in a chip increase its value as evidence?
3. What is a VIN and why is it important in forensic science?
4. In case Study 9.2, what provided a break in the case leading to identification of the suspects?
5. What trace evidence in Case Study 9.2 linked the synagogue fires to the medical building fire?