Forensic lab

What are the two different notions of the term “trace evidence”

1. related to size- small amounts of evidentiary material, often not visible by naked eye

2. something left behind

What is the definition of trace evidence

small transferable materials that can be exchanged between people, places, or objects during a crime

what are the forensic uses of trace evidence

• investigative aid (ex origin/date) of a manufactures material- geographic provenance

• association

• reconstruction

• transferred material

• pattern evidence

What is locards exchange principle

every contract leaves a trace

what are conditions that affect transfer evidence

• pressure

• nature and number of contacts

• nature of material being transferred

• degree to which material will shed/form evidence

• how much of the items is involved in the contact

What is a direct transfer

evidence transferred from a source to a location with no intermediaries

what is an indirect transfer

evidence involving one or more intermediate objects

what is primary transfer

occurs when trace evidence from a particular source is deposited directly onto another surface

what is secondary surface

when previously transferred trace evidence is transferred to yet another surface

what is tertiary transfer

when evidence is transferred three times or more

What is a non-contact transfer

when trace evidence becomes airborne and falls onto a surface

what is an example of non-contact transfer

broken glass that flies through the air onto a surface

what is pattern transfer

occurs when the material transferred may be trace evidence but the pattern imparted often has greater evidential value

what are some pattern transfer evidence

• preservation of characteristic geometric features of the donor surface

• fracture evidence (fragments to origin ex. glass)

• from contactless transfer (ex. GSR or high velocity impact spatter of blood)

• deformation of one surface by another (indentation or striations)

once the evidence transfers it will persist in that location until:

• further transfers

• degrades until it is unusable or unrecognizable

• is collected as evidence (best case scenario)

what does persistence depend on

• nature of the accepting surface

• nature of the transferred material

• environment and activity around the evidence

• time from transfer to collection

• force involved in transfer

trace evidence is often not _______ to the naked eye and often _____ at crime scenes

visible, overlooked

true or false if evidence is missed or incorrectly handled at the scene, no amount of laboratory analysis or processing will be able to rectify the problem and he scene usually cannot be revisited

true

who are some examples of people who can significantly alter the scene?

• first responders

• emergency personnel

• photographers

What are some ways to collect trace evidence

• collect the entire item containing potential trace evidence and then bringing it back to the lab to look through (ex. bedding, clothing, etc)

• picking with a gloved hand or tweezers (ex. glass, paint, hairs, fibres)

• vacuum sweeping and tape lifting (for invisible trace evidence)

• electrostatic lifting device

true or false trace evidence should be preserved to ensure no loss or damage and proper chain of custody

true

Why should clear tape be used

so it can be visualized from both sides under microscopes

when would vacuum sweeping or tape lifting be used

older crime scenes and carpets

What is questioned (unknown) evidence

evidence whereby we do not known the original source- found at the scene

what is unknown evidence

evidence whereby the origin of the sample is known

What are controls

from a known source, it is used for a comparison with unknown evidence, it is used to determine if chemical tests are performing correctly or if a substrate is interfering

How should trace evidence analysis be completed

• group items together as to whether they came from the victim, scene or suspect

• known and questioned evidence should never be analyzed together

• make note of the status of the evidence and packaging initially

• clean environment, use proper ppe

what are some analysis methods of trace evidence

• macroscopic examination

• compound or stereomicroscope

• close up photos, measurements and sketches

• determination of characteristics

What does SWGMAT

scientific working group on materials analysis trace recovery guidelines

what is the scope of SWGMAT

procedures for documentation, detection, collection, and preservation of trace evidence

What does SWGMAT do

development of guideline documents for the analysis of fibres, paint, glass, hairs, or tape; the interpretation of data; for the training new forensic examiners; and through cooperative research projects and academic exchange

what is the significance of trace evidence

associates objects, individuals, and locations; relies on proper detection, collection and preservations as well as an understanding of the mechanisms of transfer and persistence

what are some examples of guidelines produced by SWGMAT

• chain of custody beginning to end

• care to prevent contamination

• if case is multidisciplinary, confer first (what should be done to get most value)

• different locations for examination of questioned and known items to prevent contamination, should do questioned ones first

• if situation potentially compromised, document and communicate

• when selecting detection, collection and preservation techniques, and the processing sequence, consider the circumstances of hte case (use most direct and least intrusive)

how can you properly secure small/loose trace evidence

paper packets, petri dishes, glass boxes

true or false if youre air drying an object you should preserve falling trace evidence

true

if crime scene has loosely adhering trace evidence collect it _____, but if trace is firmly attached, package it ______

there, intact

true or false some types of evidence other than trace evidence may be more significant and should be given higher priority

true

how much of a representative sample is needed

a sufficient amount to show all variation in that item

patterned marks or impressions may require what scale photography

1:1

what else may be required to capture photos of trace evidence

oblique lighting, adhesive lifting, dusting, or casting

if there is a possibility of physical matching (object to source) protect edges from ______

deformation

true or false evidence must be kept in a secure location

true

what is identification

the examination of the chemical and physical properties of a substance with as near absolute certainty as existing analytical techniques will permit (ex. hair vs fibre) , number and type of tests needed to identify a substance be sufficient to exclude all others

what is comparison

an attempt to try and establish the source of evidence- do they have the same origin?

What is class evidence

placing the evidence into a group of objects with similar characteristics; associated with a common source (use of databases, and what kind of statistical weight can be assigned to a failure to exclude)

what is individualization

an object classified into a group with only one member (itself); high degree of probability

what are investigative databanks

collections of reference samples (ex. for paints, tapes, hairs and fibres, DNA, etc

what are statistical/weight of evidence databases

interpretive databases- to assign significant of class evidence which need to constantly renew in order to remain relevent

true or false trace evidence is very rarely individualized

true

what is a microscope

an optical instrument that uses a lens or a combination of lenses to magnify and resolve the fine details of an object

Which microscope has a higher objective

compound microscopes

what is a comparison microscope used for

side by side comparison

What questions can forensic hair analysis answer?

• is it hair? if so human or animal

• what area of the body

• was the hair subjected to cosmetic treatment/damage

• was the hair removed natural or forcefully

• is it a source of nuclear DNA or mDNA

What kind of evidence is hair

class evidence

what value is hair in forensics

• supplies investigative leads

• reconstructs events

• eliminates suspects

• associative evidence (dna)

true or false hair degrades quickly and is easily destroyed

false

What kind of fabrics are better for retaining hairs

rough

hairs will ______ from one area of fabric to another before being _____

migrate, lost

true or false secondary transfer of hair is possible, including during washing

true

what kind of hair(s) is most commonly used in forensic contexts

pubic or head hair

what are some examples of fabrics on heads which may retain hair

hats, balaclavas, tights

true or false there is a significant difference between human hair and dog/cat guard hair persistence

false

when may pubic hairs be transferred (at a relatively low rate)

during sexual assault

what is a hair

a slender threadlike outgrowth from the follicles of the skin of mammals

what is hair composed of?

alpha-keratins (a protein), as well as melanin (a pigment)

where does hair grow from

hair follicle

what is the part of the hair that sits in the follicle called

root/bulb

what are the three layers of hair shafts that are forensically significant

cuticle, cortex, medulla

what is the cuticle of the hair

the thin, translucent, outer protective layer that consists of scales pointing from root end to tip end of the hair

what are the cuticle structure types

• crown like-coronal

• petal like- spinous

• flattened- imbricate

true or false structure types are not useful for differentiating human hair but becomes useful for species identification of animal hair

true

what is the cortex of the hair

the portion of the hair between the medulla and cuticle which makes up a majority of the hair, composed of elongated cells parallel to the length of the hair

what part of the hair contains pigment granules

the cortex

why are pigment granules forensically significant

for comparison of colour, shape, and distribution of granules

what are cortical fusi

air vacuoles and ovoid bodies (occasionally found in the cortex of hair)

what is the medulla of the hair

the core

what are guard hairs

outer coats of animals, typically longer and stiffer

what is an example of a guard hair

the long hair on a dog that sheds

what is fur

inner coat of an animal, often fine and uniform in shape but not often used in forensic context

what are tactile hairs

hairs like whiskers that are longer and stiffer but not commonly encountered

true or false human hair is as differentiated as animal hairs

false

human hair is relatively consistent in colour and _____

pigmentation

terminal hairs of humans (head and pubic hairs) are _________ visible

macroscopically

Where are cuticles that are coronal usually found?

in hairs of very fine diameter

how do coronal cuticles look?

like stacks of paper cups

what animals have coronal cuticles?

small rodents and bats

what do spinous cuticles look like

petal like scaales approximately triangular in shape that protrude from the hair shaft

what animals have spinous cuticles

minks, seals, and cats

what do imbricate cuticles look like

flattened scales with narrow margins

what animals have imbricate cuticles

humans, elks, and raccoons

where is pigment distribution in the cortex?

toward the cuticle (except in red heads)

what medulla patterns can humans have?

• absent

• fragmentary/trace

• discontinuous/interrupted

• continuous

what is the medulla structure of humans

amorphous

what does amorphous mean

no real pattern

what is the medullary index

the diameter of the medulla/ the diameter of the shaft

what is the medulla index for humans

less than 1/3

what is the medulla index for animals

½ or greater

do animals medullas have patterns and structures that are not amorphous

yes

how can human hair and animal hair be macroscopically distinguished

only animal hair exhbitis multiple abrupt colouration changes known as banding and some animals have contour patterns like zigzags not seen in humans

how can human hair and animal hair be distinguished microscopically

the cuticular scale as humans cuticles lie close to the surface of the hair and tends to protrude less and the pigment is only found within the cortex of human hair instead of both cortex and medulla like animal hair