Forensic Science: Fundamentals & Investigations, Chapter 15 1 Kendall/Hunt Publishing Company1 Trace Evidence, Casts, and Impressions “Breadth of view

Forensic Science: Fundamentals & Investigations, Chapter 15 1 Kendall/Hunt Publishing Company 1

Trace Evidence, Casts, and Impressions

“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

Forensic Science: Fundamentals & Investigations, Chapter 15 2

Trace Evidence, Casts, and Impressions By the end of this chapter you will be able to:

distinguish between patient, latent, and plastic impressions

describe how to make foot, shoe, and tire impressions

use track width and wheel base information to identify vehicles

prepare dental impressions and match them with bite marks

Identify lipstick through chromatographyAll Rights Reserved South-Western / Cengage Learning © 2009

Forensic Science: Fundamentals & Investigations, Chapter 15 3 Kendall/Hunt Publishing Company3

Trace Evidence

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.

How to apply deductive reasoning to analytical data.

How to follow qualitative analytical schemes.

How to gather and use information to solve problems.

Students will be able to:


Trace Evidence

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.


Unusual Types ofTrace Evidence

A torn piece of paper

Itching powder Ashes A spider A match Grease Linoleum


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.


Metal Analysis

Bits of metal can be identified from their physical and chemical properties.

Solid particles—microscopic examination, magnetism, malleability, density, color, solubility, reactivity, hardness

Dissolved metals—separation by chromatography with comparison of Rf values to known metals, specific reactions and color tests


Metal Analysis

Microscopic examination: look at structure of fragments, distinctive marks on the fragments, other visual patterns

Magnetism: attraction or repulsion to magnetic material, or unaffected by magnetic material

Malleability: capable of being shaped, bent or drawn out; flexible Density: ratio of mass to volume, identifying characteristic of a

material Solubility: ability to be dissolved in a solvent (use a variety of

solvents) Reactivity: determine what kinds of materials cause a chemical

reaction, and observe strength of the reaction Hardness: ability to be scratched

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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.


Qualitative Analysis

Microscopic Examination


Qualitative Analysis

Solubility

pH (acid, base or neutral)

Chemical reactions Color Precipitate formation: precipitates are solids

formed in a chemical reaction Evolution of gas: gases are formed as a result of a

chemical reaction.


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.


Casts and ImpressionsCasts and Impressions

People, vehicles, and objects leave evidence of their presence at an accident or crime scene.

Patent impressions are two-dimensional. Latent impressions are hidden to the eye. Plastic impressions are three-dimensional.


Shoe Impressions Shoe Impressions

The size of a shoeprint can tell the size of foot of the person.

The depth of a foot or shoe impression can tell something of the person’s weight.

The type of shoe can tell something of the person’s job or personality.

Databases contain the names of specific manufactures and tread patterns used to identify different types of shoes.


Shoe Wear Patterns

Some factors that personalize a person’s footwear include: – Body weight. – The way a person walks. – The surface on which the person usually

walks. – Debris that became embedded in the tread or

unique holes and cuts in the tread.


Collection of Shoe Impression Evidence

Why would the following steps be important?

1. Take photos as soon as possible. 2. Take multiple photos of the impression from

at least two different orientations. 3. Place an identifying label and a ruler in

position with the impression for the photo. 4. Use oblique lighting when possible.


Lifting Latent Impressions

Different methods to make latent prints visible include: Luminol will make bloody footprints visible. Dusting the latent print reveals an impression. Electrostatic lifting and gel lifting (impression

shown above) techniques also can capture hidden impressions.


Electrostatic Dusting and Lifting

Electrostatic dusting can reveal dust left with each step and create an impression.

Electrostatic charges can lift impressions from paper, carpeting, wood surfaces, linoleum, asphalt, and concrete.


Tire Treads and Impressions Tire Treads and Impressions

To channel water away and provide traction, a tire’s tread is divided into ridges and grooves.

Tires can leave patent, latent, or plastic tread patterns.

Tire evidence usually indicates the type of vehicle that left the mark, may be used to link a suspect or victim to a crime scene, and can reveal the events that took place.


Recording Tread Impressions

Ridges and grooves of discovered tire impressions are counted across the entire width.

Unique characteristics such as wear or pebbles embedded in the grooves are noted.

A print of a suspect’s tire impressions (through one revolution) is taken.


Identifying a Vehicle

Identifying tread patterns may not be enough to link a suspect with a crime scene. Other things can help with this: – Front and rear track widths. – Wheelbase measurement. – Turning diameter.

Databases can be checked to find the vehicle with these specifications.


Accident Reconstruction

Drivers may not recall the exact series of events before, during, and after an accident.

People, vehicles, and objects, however, can leave evidence of their actions at the scene of an accident.

Debris patterns and tire marks, for example, can be clues to speed, direction, and vehicle identification.


Accident Reconstruction

There are three basic types of tire marks:

Skid marks—can be clues to the distance when brakes were applied and the vehicle’s speed.

Yaw marks—can show a sideways skid.

Tire scrub—can determine the area of impact.



Note “yaw” marks on roadway. Marks on the right are from the rear tires and marks on the left are from the front tires just prior to the rollover. Tire yaw marks occur when a vehicle slides sideways while still moving forward. In a true yaw, where the vehicle’s rear is attempting to pass the vehicle’s front, each rear tire tracks outside the corresponding front tire. (Photo Courtesy of County Sheriff’s Office)


Dental Impressions Dental Impressions

Occasionally a perpetrator will leave behind a bite mark.

Differences in the size of teeth and jaws, position, fillings, crowns, caps, breakage, and crowding make bite marks individual evidence.


Dental Patterns in Forensics

The investigation consists of recognizing, documenting, collecting, and analyzing evidence.

Up to 76 points of comparison can be used when comparing a suspect’s dental patterns with bite marks left at a crime scene.


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


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?

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Lip Prints

Lip prints are different and can be used to identify suspects. There are several general patterns:


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.


Lipstick Chromatography

A prosecutor’s witness was having a drink in a busy restaurant. A waiter noted that he was soon joined by a woman with dark hair, wearing sunglasses. The waitress brought her a drink and was surprised to see her leave shortly afterwards.

The waitress noticed that the witness looked like he had fallen asleep, but she soon discovered that he was dead. A key piece of evidence was a lipstick smudge on a napkin at the scene.

Seven women were picked up shortly afterward near the restaurant. Two women had red lipstick, one had purple lipstick, and two wore no lipstick, but had tubes or red in their purses. Three of them were wearing dark glasses.

Can we match the lipstick left at the scene to one of the suspects?

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Forensic Science: Fundamentals & Investigations, Chapter 15 1 Kendall/Hunt Publishing Company1 Trace Evidence, Casts, and Impressions “Breadth of view