Download File - Ms. Collins forensic science

Warm-Up
Can you identify the mystery items?
All the items are associated with crime scene
investigations.
#3
#1
#4
#2
The answers are …
#3
#1
#4
#2
Pollen and Paint Evidence
Palynology
 The study of pollen and spores
 Important to know:
 What is produced in a given area
 The dispersal pattern
 Variation in size and weight
4
Palynology
•
Since both pollen and spores have resistant
structures, they at times can help determine
such things as whether a body was moved, a
crime’s location, whether it occurred in a city
or in the country, or in which season it may
have occurred.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
5
Pollen-Producing Plants
•
Pollen-producing plants provide a pollen fingerprint—a
•
specific type of pollen grain.
A certain number of grains are found in a specific
geographical area during particular times of the year.
– Examples of non-seed plants would be ferns,
mosses, liverworts, and horsetails.
– Examples of seed plants would be gymnosperms
(cycads, ginkgoes, and conifers like an evergreen)
and angiosperms (flowering plants like roses).
Forensic Science:
Fundamentals & Investigations,
Chapter 5
6
Gymnosperms
•
Gymnosperms are the oldest seed
plants.
• Evergreens are conifer
gymnosperms.
– seeds in a hard, scaly structure
(cones).
• Pollination occurs when pollen is
transferred from the male cones to
the female cones.
• Which of the two structures
shown above transfers pollen to
the other?
Forensic Science:
Fundamentals & Investigations,
Chapter 5
7
Angiosperms
Petal
Anther
Stigma
Style
Filament
Ovary
with seeds
Sepal
• The most recent plant group to evolve is known as the
flowering plant.
• Identify its different parts in the illustration above.
– Stamen (Male parts: Anther, Filament)
– Pistil (Female Parts: Stigma, Style, Ovary)
• Plants in this group produce seeds in an enclosed fruit.
• These plants are very diverse and include corn, oaks,
maples, and the grasses.8
Forensic Science:
Fundamentals & Investigations,
Chapter 5
Types of Pollination
Pollination is the transfer of pollen
from the male part of a plant to the
female part of a seed plant.
– Self-pollination, in flowering
plants, involves transfer of pollen
from an anther to the stigma
within the same flower, as in pea
plants.
– Cross-pollination (illustrated
above) involves two distinct
plants.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
9
Types of Pollination
• Pollen of self-pollinating plants is generally
of lower value in forensic studies because it
is rarely encountered.
• Pollen can be carried by wind, animals, or
water.
• Pollen carried by wind may be less effective
for determining direct links between
individuals and places because of the long
distances over which it can be carried.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
10
Spore Producers
• Spore producers include certain protists
(algae), plants, fungi, and the bacteria that
produce a unique type of spore.
• Bacterial spores, endospores, can cause
diseases such as anthrax and botulism.
• Spore analysis has the advantage that the
spores possibly can be grown and the species
identified with certainty.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
11
Spore Dispersal
Cap
• Algae disperse spores into
water or air.
• Spore producers have the
same value in
investigations as pollen
from wind-pollinated
Gills
plants.
• Identify the different parts
of the mushroom
illustrated above and
Stem
explain how its spores are
released into the wind.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
12
Ring
Volva
Pollen and Spore Identification in
Solving Crimes
•
•
•
Angiosperm pollen grains
Gymnosperm pollen grains
The outer shell of a pollen grain and spore (the exine) has a
complex and unique structure.
These are revealed under a microscope.
Identification can provide important trace evidence in solving
crimes.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
13
Finding Pollen and Spores
Forensic Science:
Fundamentals & Investigations,
Chapter 5
14
How to Collect Pollen and Spores
• During an investigation, control samples must be
collected as well as evidence samples.
• Samples must be collected wearing gloves and with clean
tools (such as brushes and cellophane tape) and placed in
sterile containers, which then must be sealed and labeled
with care.
• Sampling instruments must be cleaned after each use, or
new ones must be used.
• Collected evidence must be secured, and the chain of
custody must be maintained.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
15
Analyzing Pollen and Spore Samples
• To identify pollen and spores, specialists can use a
compound light microscope, a scanning electronic
microscope, reference collections that may consist of
photos and illustrations or perhaps even actual dried
specimens arranged systematically (herbariums).
• Pollen and spore evidence that has been collected,
analyzed, and interpreted can be presented in court.
• These “fingerprints” can be used to confirm certain
aspects of a crime.
Forensic Science:
Fundamentals & Investigations,
Chapter 5
16
Paints and Coatings
Introduction
• Chemistry of paint very complex
• Forensic role is to compare paint
evidence from scene to known source
• Individual evidence only in cases where
large enough paint samples exist to
physically match
Definitions
• PAINT: A suspension of pigment in a film
former (also called vehicle)
– Usually not a solution. Pigment is suspended in
film former
– Pigment is usually mixture of inorganic metal
salts. Purpose is to impart color.
– Film former is usually organic polymer(s).
Purposes are to protect surface and hold pigments
What are some of the uses for paint?
• Art works
• Decoration (residential paints)
• Protection of a surface (rust inhibiting auto
paints)
• Warnings (reflective paint, fluorescent paint)
Paint Cross Section
Other Coatings
• Varnish: A film former, commonly polyurethane,
dissolved in a solvent, which normally doesn’t
contain a stain. Purpose is to protect wood
• Stain: A mixture of organic dyes dissolved in solvent.
Made to penetrate wood and stain in. Does not
protect
• Enamel: originally a glossy, thermosetting paint.
Now any paint which dries glossy
Paint As Evidence
• Paint chips: Pieces of paint which have come
off surface. They usually contain all of the
layers of the paint
• Paint smears: The top layer of paint which
has loosened owing to being wet or air
oxidation. Smears onto another surface after
brushing contact. Layer structure is not
present
Analysis of Paint
• Color layer analysis
– Requires cross section of paint chip
– Cannot be done on paint smears
– Same number and order of layers
– Relative thickness must be same
– Is a class test (but see case at end of lecture)
Paint Cross Section
Analysis of Paint
• Solubility
– Use solvents such as acetone,
dichloromethane, pyridine. Acrylic lacquers
are soluble in acetone
• Pyrolysis GC
– Analysis of film formers
– Bulk technique, all layers analysed together
Pyrolyzing Unit
Analysis of Paint
• Pyrolysis GC
Analysis of Paint
• FTIR
– Fourier transform infrared spectroscopy
– Collects spectral data (absorption, emission,
etc.)
– Will determine type of film former
– Does not show pigments unless they are
organic
– Is a bulk method: if more than one layer is
present, IR will be a composite
FTIR of Automobile Paint
Analysis of Paint
• Electron microscopy
– Inorganic pigments
– Excellent for single, top layer analysis and paint
smears
• UV-visible spectrophotometry
– Must be able to separate pigment from film former
and dissolve it
The Case of the 11 Layer Paint Chip
•
•
•
•
Hit and run case
Paint chips left at crime scene on victim
Chips had 11 distinct layers of various colors
Samples taken from suspect auto showed 11
layers with matching color-layer sequencing
The Case of the 11 Layer Paint Chip
• Paint examiner testified that paint found at
scene CAME FROM THE SUSPECT CAR
(individualized chip to car)
• Defense attorney asked examiner the
following hypothetical question: “What would
your conclusion have been if there had been
only 10 matching layers?”
The Case of the 11 Layer Paint Chip
• Where is the defense attorney going with this
line of questioning?
• Why does this question present a problem for
the examiner?
• How would you answer defense attorney’s
question?
The Case of the 11 Layer Paint Chip
• One possible answer to question: “I cannot
give you a definitive answer. I take each case
on an individual basis and reach a conclusion
based on the evidence in that case. It would
not be possible to generalize about an optimal
number of layers of paint that are present.”