Fs Ch 13

Chapter 13

Trace Evidence II: Paint, Glass, and Soil

Forensic ScienceRichard Saferstein

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

All Rights Reserved.2

Paint Most common:

-automobile paint finishes

-multiple coatings

-electrocoat primer/primer surfacer/basecoat/clearcoat.




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




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




Paint Comparison




Microscopic comparison




The Lab




Trace




Collection and Preservation Paint chips:

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




Glass Fragments Amorphous substance:

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




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




Flotation Method Glass densities:

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




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




Analyzing Cracks radial fractures

concentric fractures

-direction of impact.




Radial fractures

Concentric fractures




Looking at end of broken pane of glass

CONCENTRIC FRACTURES




End of broken piece of glassRADIAL FRACTURES




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




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.




Collection of Glass Find all the pieces

On suspect

Representative known sample

solid containers

individually wrapped in paper




Soil Value:

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




Removing evidence from sole of boot




Foot wear impression compared to shoe

Tire wear impression compared to tire




Removing shoe evidence




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




It’s hard to get ahead.




Homeless camp in the desert with multiple victims




Does crime scene processing still seem as glamorous as CSI?




Comparison of Soil Forensic geologists:

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




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

Fs Ch 13

Technology

Transcript of Fs Ch 13