CTE Forensics/Law & Public Safety 1-2 Unit 4 Trace Evidence I: Hairs and Fibers.
TRACE EVIDENCE II: METALS, PAINT & SOIL Forensics.
-
Upload
evelyn-godfrey-robbins -
Category
Documents
-
view
291 -
download
1
Transcript of TRACE EVIDENCE II: METALS, PAINT & SOIL Forensics.
TRACE EVIDENCE II: METALS, PAINT & SOIL
Forensics
Forensic Examination of Metal Anything present in concentrations of
less than 1% is considered a trace element
These trace elements can provide invisible markers that can establish the source of an item
See page 389, Table 11-1
Who Killed JFK?
Did Lee Harvey Oswald work alone or was he part of a conspiracy?
The Warren Commission - government agency that decided Oswald worked alone Still a controversy
The Warren Commission’s Reconstruction Oswald was hidden on the 6th floor of a
nearby building. He fired 3 shots from behind the president. 1 bullet totally missed the president 1 bullet hit the president in the back, exited
his throat and went on to hit Governor Connally in the back, wrist and thigh
1 bullet lodged in the president’s skull Found in the building were 3 cartridge
casings
Questions & Criticisms
Some people believe some shots were also fired from the grassy knoll in front of the car
Some people also argued that the bullet from the Governor’s thigh and wrist couldn’t be the same bullet that went through the president’s back. The recovered bullet did not show enough deformation
The Forensics
14 years after the assignation forensics was used to determine trace elements in the bullets and bullet fragments found P 390 Table 11-2
There is evidence of only 2 bullets There were no bullet fragments
associated with the wound in JFK’s back, so they couldn’t definitively link those wounds to the bullet from the Governor.
Atomic Structure
Particle SymbolRelative Mass
Location Charge
proton 1
neutron 1
electron 1/1837
Atomic Identity
The atomic number gives an atom its unique properties and behaviors
Atomic number = number of protons in an atom
Isotopes
Isotopes - atoms with the same number of protons but different numbers of neutrons This only changes the MASS of the atom, not its
properties or identity Example: Hydrogen
Ordinary hydrogen - mass of 1 Deuterium - mass of 2 Tritium - mass of 3
Most elements have several isotopes. Many isotopes are stable, but some decompose over time through radioactive decay
Radioactivity
Radioactivity - the emission of energy/particles when a nuclei breaks down
Three types: Alpha rays - helium nuclei (no electrons) Beta rays - electrons Gamma rays - electromagnetic radiation
In a nuclear reactor atoms are hit with neutrons. This makes new isotopes that are radioactive and decompose to produce energy
Neutron Activation Analysis
In forensic labs, trace elements can be identified using neutron activation analysis
The specimen is hit with neutrons and the resulting gamma rays are measured
Each element has a unique set of radioactive isotopes that can be formed and those isotopes release a unique level of energy in the gamma rays they release during decomposition.
Forensic Examination of Paint Paint evidence is used in many crimes
but is typically the most useful in hit-and-runs and burglary cases
Still important to have reference samples to compare to the paint evidence
Thanks to databases like PDQ, a forensic scientist can frequently determine the make, model and color of a car from paint chips
Composition of Paint
Paint is composed of a binder and pigments Pigments - give color and some other properties Binder - supports the pigments and keeps them on
the surface 4 coatings to automobile paint:
Electrocoat primer - provides corrosion resistance Primer surfacer - smoothes & hides seams/flaws Basecoat - provides color and special finishes Clearcoat - adds gloss and durability
Microscopic Examination of Paint Compare:
Color, surface texture and color layer sequence
Color layers are the most important but still are considered class evidence in most cases
Must use chemical composition of paints to individualize paint evidence
Analytical Techniques for Paint There are several ways to analyze the
composition of paint evidence Characterization of Paint Binders Characterization of Paint Pigments Inductively Coupled Plasma Emission
Spectrometry
Characterization of Paint Binders Pryolysis Gas Chromatography - (p398
Fig 11-7) paint samples are broken down with extreme heat and added to a carrier gas. The gas is then sent through a column which separates the individual elements. P 399 Figure 11-8
Infrared Spectrophotometry - binders selectively absorb IR radiation differently
Characterization of Paint Pigments Three ways to identify the chemicals in paint:
Emission spectroscopy, neutron activation analysis and x-ray spectroscopy
Emission spectroscopy is able to detect 15-20 elements at once. Atoms are ‘excited’ with energy, causing e- to jump energy levels. As they fall back down they release energy. The amount of energy released corresponds to a color of light
Emission spectrum - the light a source emits broken into its component colors Continuous - the rainbow Line spectrum - series of lines with black spaces P. 400 Fig 11-9
Inductively Coupled Plasma Emission Spectrometry (ICP) A spark is applied to argon gas in a
plasma torch This spark takes some e- from the argon
atoms and these e- are accelerated to collide with other argon atoms to take even more e-
The gas sample is then introduced to the argon plasma and generates ions
The ions produce light that corresponds to the elements in the sample
How Significant is Paint Evidence? Many cars are the same color. However, the binders and paint
composition may be different at the chemical level
Databases allow forensic scientists to identify the make and model of cars from very small paint samples
Collection and Preservation of Paint Evidence Pick up paint evidence with tweezers or
scoop it up with a piece of paper Package the whole piece of paint Collect several reference samples (from
undamaged areas of questionable cars) Make sure reference samples include all 4
layers of paint Page 407 - Case Study - The Predator
Forensic Analysis of Soil
In forensics soil is considered ANY small pieces of surface material, natural OR artificial
Soil Evidence can be significant because it is so easily transferred Can lead investigators to specific locations
Forensic Examination of Soil
Microscopic - reveals plant and animal materials as well as artificial debris Requires a scientist trained in geology Compare the minerals and rocks found Compare the building/artificial materials
Density-Gradient Tube - allows soil to be separated by density Heaviest particles sink to the bottom
Variations in Soil
If the soil around a crime scene is similar to other soil it is not very useful
Soil can only be individualized to a specific location when it includes an unusual combination of components.
Collection & Preservation of Soil Evidence Collect reference samples in a 100-yard
radius of the crime scene. Must be careful to only sample the top
layer of soil Soil evidence should not be removed
from the item it is found on. The entire item should be wrapped up and sent to the lab
Page 413 - Forensic Brief
The CBS Murders
Read the Case Reading on Page 419-421 Answer the Case Analysis Questions of p
416