Trace Evidence Flashcards
describe R v Smith 2007
- intruder used the butt of a rifle to break the window of a front door
- then reached in and opened the front door
- then shot and killed James Smith
true/false a piece of plastic the size of a quarter helped police solve a 2000 murder
true
how did a piece of plastic the size of a quarter helped police solve a 2000 murder
- a girl was hit by a car and dragged into the woods and laid into a puddle and she drowned
- they found shards of glass and a little plastic piece
- the plastic told them the car was an early 1990s Ford Tempo
- PO then found a ford tempo that was missing a piece of plastic
Forensic analysis of glass consists of what
exam of two or more fragments to determine whether they have a common origin
Identifying broken glass fragments having a common source to the exclusion of all other sources may only be done if they can be what
physically matched togegther
what is the most common and important material submitted for forensic trace evidence
glass
what is the composition of window/ bottle glass
- soda lime
- sodium carbonate
- calcium carbonate/ calcium oxide
- silicon oxide
- Na, Ca, Mg, K, Si, O, C
what is the composition of automobile headlights/ heat resistance glass
- Silicon oxide
- boron (B)
true/false glass fragments that may remain on clothing for a long time are very stable
true
what does Ri stand for
refractive index
what is differentiating glass from plastic done
- by examining relative
- hardness,
- solubility,
- observation with a polarized light microscope
Once confirmed as glass, the examiner will do what
- perform an analysis of physical properties (color, fluorescence, thickness, curvature, density),
- optical properties (Refractive Index) and
- chemical composition
what is the order in which glass is analyzed
- confirm it is glass
- analyze physical properties, optical properties, chem composition
true/false If a difference between questioned and known samples is found at any point, no further comparison is needed
true
what are the challenges associated w comparing glass fragments
- Most glass evidence is either too fragmentary or too minute to permit a comparison of this type
- Search for individual properties may be fruitless
- The general chemical composition of various window glasses within the capability of analytical methods has found to be relatively uniform among various manufacturers - no basis for individualization
what causes differences in the physical and chemical properties of glass
- Different methods of production
- variations in composition of the raw materials
what main physical properties are used to compare glass
- refractive index
- density
true/false Ri and density are class characteristics
true
true/false Ri and density cannot provide the sole criteria for individualizing glass to a common source
true
is there an Ri. database
- they’re working on it
- the FBI did a bit
the Ri value of 1.529 discovered by the FBI was found in how many samples
1 in 2200
the Ri value of 1.5180 discovered by the FBI was found in how many samples
22 in 2200
true/false the biggest issue w trace evidence is finding and quantifying it
- false
- its transfer and persistance
if there was a car crash and the perp abandoned the car, where should we look for glass
- laundry (clothing)
- sofa/ chair in living room
- entryway (could be on shoes)
- bathroom sink (when cleaning themselves off)
in her case example of the hit and run, what was the result of the glass they found at his house and the car
- evidence was “indistinguishable”
- aka a match
what did the study about glass and pant presence on the clothing and footwear of random people tell us
- more glass was found in the winter than the summer (7% vs 0.9%)
- about 26% of the clothing was on the upper surface
what is found in paint
- pigments (for colour)
- binders/ additives
what are the diff layers of paint
describe the first layer of paint
- electrically applied coat (e-coat)
- 1st layer
- applied directly to car
- epoxy-based, a polymer or resin
- black or grey colour
describe the second layer of paint
- primer
- second layer
- epoxy-based
- polyester chemical or urethane chemical
- white or pigmented (made to layer well w basecoat)
describe the third layer of paint
- basecoat
- third layer
- what gives the car colour
- acrylic polymer
- also has a binder to hold the paint in place
(stops from peeling)
describe the fourth layer of paint
- clearcoat
- 4th layer
- gives the car a glossy finish
- uncoloured or transparent
- acrylic polymer or polyurethane polymer
how many layers are in a car paint
- most common is 4 (81%)
- sometimes 5 31%
what is looked at at a microscopic exam of paints
- colour,
- surface texture,
- colour layer sequence (number and colour of layers)
true/false each production plant may use one paint supplier for a particular colour or vary suppliers during a model year
true
describe the Center of Forensic Science-Paint-Case study
- they testsed 260 paint chips from a wreck yard
- looked at colour and number of layers via a microscope
- all samples were distinguishable
what are the odds of CS paint originating from another randomly chosen car
30 000 : 1
what is the PDQ
paint data query
what does the PDQ allow analysts too do
- obtain information on paints related to automobile
- make
- model
- year
what info does the PDQ have that allows analysts to get all this info about the automobile from a paint sample
- colour of paint
- colour of primer
- layers
- binder chem composition
what is OEM
original equipement manufacturer
what is key in the language that is used by experts regarding paint exams
- they “could” have come from the known source
- no info on the likelihood or frequency
- can have data to quantify the evidentiary value, but no exact numbers
what are the possible outcomes for paint evidence in expert opinion
- differentiated (distinguishable)
- not differentiated (analytically indistinguishable)
what should courts know regarding expert opinion
- rarity of the transferred paint how significant are the findings
- if the characteristics of the transfer of paint are commensurate w the alleged activity a calm break and enter wont result in someone covered head to toe in paint.
fibers can assist in drawing what conclusions
- contact that has occurred
- how the contact was made
- how recently that contact took place
what is the goal of forensic examination of fibers
narrow down the origin to a limited number of sources or even to a single source
what is the challenge of forensic examination of fibers
mass production of garments and fabrics - limited value of fiber evidence
what is the difference between class I and class II fibers
- natural
- manufactured
what are some natural fibers
- hair (human or animal)
- cotton: plant based source
- wool: animal based source
what are some manufactured fibers
- polyester
- acrylic
- nylon
- spandex
what is the most commonly used thing to examine fibers
optical microscopy
what do we use optical microscopy for
comparison of standard/reference fibers
what is noted when comparing fibers
- Colour
- morphological characteristics,
- diameter,
- striations,
- pitting,
- particles presence
true/false optical microscopes can differentiate fibers w the same colour
false
what is the order of examining fibers
- optical microscopy (colour, diameters, striations etc)
- dye composition
- chem composition
what do we look for when comparing the chem composition of diff fibers
- diff chem structures
- polymeric structure
what is level 1 vs level 2 chem composition comparisons
- level 1 Confirm that all fibers involved belong to the same broad generic class
- level 2 Confirm that all fibers belong to the same subclassification within their generic class
what are individual characteristics of shoe prints/ tire tracks
-cuts, scratches, gouges, holes, or
-random inclusions that result from manufacturing, such as bubbles, and
-those that result from adherent substances, such as rocks, chewing gum, papers, or twigs.
true/false shoeprint databases exist
yesrue
describe the R v Mercer 2007 case
- 30cm from victims head (larochelle), there were 2 bloody partial shoeprints
- PO matched these to mr mercer’s sandles
what does “identification” mean
definite conclusion of identity
what does “probably made” mean
very high degree of association
what does “could have made” mean
significant association of multiple class characteristic
what does “inconclusive” mean
limited association of some characteristics
what does “probably did not make” mean
very high degree of nonassociation
what does “elimination” mean
definite exclusion
what does “unsuitable” mean
lacks sufficient detail for a meaningful comparison
describe how tire tracks were used in the testimony at the Aaron Hernandez trial
- four stones were in the rear passenger side tire of a car he used
- this created an “anomaly” in the tread pattern
describe how tire tracks were used in the Jacob Wetterling case
- there were a myriad of tire tracks and shoe prints where he was last seen
- Danny Heinrich’s tires were used for search warrants
- Heinrich had just confessed to an unrelated murder as part of a plea, and turned over his shoes and the tires of his car
- the FBI lab found a “general match” of these prints
- they corresponds in design but due to lack of sufficient detail an exact match could not be made
describe the R v Hilaire 2018 case
- Nevin was struck by a ford pickup truck when riding his bike
- he died instantly
- they found paint chips on his undershirt, tshirt
- these paint chips were similar in all aspects to the paint in the hood of the truck
- they found fibers in the right front quarter panel of the truck and hood of the truck, matching his shorts and udnerwear
