Trace Evidence: Analyzing Physical and Chemical Properties for Forensic Investigation

1. Chapter 9Trace Evidence “Breadth of view is one of the essentials of our profession. The interplay of ideas and the oblique use of knowledge are often of extraordinary interest.” —Arthur Conan Doyle’s Sherlock Holmes, in The Valley of Fear Kendall/Hunt Publishing Company

2. Trace Evidence Students will learn: • How to apply deductive reasoning to analytical data. • How to follow qualitative analytical schemes. • How to gather and use information to solve problems. Kendall/Hunt Publishing Company

3. Trace Evidence Students will be able to: • Identify metals. • Identify traces of white powder. • Classify lip prints. • Use chromatography to compare lipsticks. • Design and conduct scientific investigations. • Identify questions and concepts that guide scientific investigations. Kendall/Hunt Publishing Company

4. Trace evidence is physical evidence found in small amounts at a crime scene. Common examples would be 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 Kendall/Hunt Publishing Company

5. A torn piece of paper Itching powder Ashes A spider A match Grease Linoleum Unusual Types ofTrace Evidence Kendall/Hunt Publishing Company

6. Physical andChemical Properties Physical property: A characteristic that does not involve a change in the identity of a substance, such as odor, color, boiling point, density, refractive index. Chemical property: A characteristic that determines how a substance will change into another substance with different physical properties. Kendall/Hunt Publishing Company

7. Metal Analysis Bits of metal can be identified from their physical and chemical properties. • Solid particles—microscopic examination, magnetism, malleability, density, color, solubility, reactivity • Dissolved metals—separation by chromatography with comparison of Rf values to known metals, specific reactions and color tests Kendall/Hunt Publishing Company

8. Product Liability 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. Kendall/Hunt Publishing Company

9. Analysis of Metal Particles Kendall/Hunt Publishing Company

10. Environmental Contamination 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 Kendall/Hunt Publishing Company

11. Environmental Pollution The metals were identified, but where did they come from? • A magnet manufacturer? • A maker of brass hardware? • A rechargeable battery company? Kendall/Hunt Publishing Company

12. Trace Evidence: Qualitative Analysis 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. Kendall/Hunt Publishing Company

13. Qualitative Analysis Microscopic Examination Kendall/Hunt Publishing Company

14. Solubility pH Chemical reactions Color Precipitate formation Evolution of gas Qualitative Analysis Kendall/Hunt Publishing Company

15. A Historical Crime In 1912, Emile Gourbin was a bank clerk in Lyons, France. He came under suspicion of strangling his girl friend, Marie Latelle. Gourbin was arrested but had what appeared to be an air-tight alibi. Edmond Locard went to Gourbin’s cell and removed scrapings from under his fingernails. The scrapings 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. Examination of the 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. Kendall/Hunt Publishing Company

16. A More Recent Crime 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. http://www.hbo.com/autopsy/episode/episode_6_the_telltale_imprint.html Kendall/Hunt Publishing Company

17. Lip Prints Lip prints are different and can be used to identify suspects. There are several general patterns: Kendall/Hunt Publishing Company

18. Lip Prints What happened? 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. How? Kendall/Hunt Publishing Company

19. Chromatography of Lipsticks Thin layer chromatograph (TLC) can be used to separate the components of a lipstick. The chromatograms can then be compared for a match. Kendall/Hunt Publishing Company