fs ch 13

Chapter 13

Trace Evidence II: Paint, Glass, and Soil

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Paint Most common:

-automobile paint finishes

-multiple coatings

-electrocoat primer/primer surfacer/basecoat/clearcoat.

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Methods for Paint Comparison Diversity:

-forensic significance-questioned and known specimens-stereoscopic microscope: color/surface texture/color layer sequence-pyrolysis gas chromatography/infrared

spectrophotometry: paint binder formulations

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Methods for Paint Comparison Solid:-heated (pryolyzed)-decompose into gases-GC column -small amounts of paint-ID make/model of car-PDQ data base

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Paint Comparison

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Microscopic comparison

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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The Lab

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Trace

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Collection and Preservation Paint chips:

-persons or objects-hit-and-run incidents.-paper druggist folds/vials -garments/objects smeared -standard/reference -tools

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Glass Fragments Amorphous substance:

-silicon oxides-metal oxides-random atoms-tempered glass-laminated glass

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Glass Fragments Problem:-association -minimizing/eliminating sources Comparison:-density -refractive index

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Flotation Method Glass densities:

-immersed in liquid-density adjusted by-chip remains suspended -same density as liquid -compared to other glass-suspended/sink/float

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Immersion Method Refractive index:

-glass particle in a liquid -refractive index is varied-equal to particle-match point-Becke line: bright halo near the border of

particle -Becke Line disappears

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Analyzing Cracks radial fractures

concentric fractures

-direction of impact.

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Radial fractures

Concentric fractures

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Looking at end of broken pane of glass

CONCENTRIC FRACTURES

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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End of broken piece of glassRADIAL FRACTURES

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Analyzing Cracks

Directionality:

High-velocity:-wider at the exit side -3 R rule:Radial cracks form a Right angle on

the Reverse side of the force-terminates at existing line of fractures

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Projectile hole

Formation of a bullet hole in a pane of glass. Note the crater form of the hole and the arrow shows the direction of the bullet.

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Collection of Glass Find all the pieces

On suspect

Representative known sample

solid containers

individually wrapped in paper

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Soil Value:

-prevalence at scenes-transferability-easily differentiated-side-by-side visual comparison: color texture different locations

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Removing evidence from sole of boot

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Foot wear impression compared to shoe

Tire wear impression compared to tire

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Removing shoe evidence

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Jaw bone in the dirt-nightmare for trace evidence/contamination

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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It’s hard to get ahead.

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Homeless camp in the desert with multiple victims

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Does crime scene processing still seem as glamorous as CSI?

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Comparison of Soil Forensic geologists:

- Compare mineral content-vast variety of minerals/rocks -artificial debris -points of comparison

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Collection of Soil Standard /reference:-various intervals-100-yard radius -site of the crime

on suspect:-shoe/garments-must not be removed -wrap individually in paper-lab