CRIM 355

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  1. Science Chemistry
    • Science of the everyday
    • Study of NON-BIOLOGICAL trace evidence
    • Locard’s Exchange Principle
    • E.g. paint, glass, fibres, drywall, glue, cleaner fluid, adhesive tape etc.
    • Crime scene? – ordinary people, ordinary place
    • E.g. criminal in woolly sweater,  victim’s makeup, duct tape, bomb, materials
  2. Forensic Chemist’s analyze
    • Anything that is not a body fluid
    • Used to be part of hair and fibre (still is in US).
    • Now: fibre – chemistry
    • hair - biology
  3. Qualifications
    • B.Sc. Honours (minimum)
    • Chemistry – lots!
    • All basic analytical techniques
    • Civilians
    • Then basic training in lab under a mentor ~ 15-18 months
    • Mock trial
  4. Types of Crimes
    • B & E
    • broken glass,
    • fragments of drywall

    • Hit and run
    • Car light glass
    • Car lights
    • Paint

    • Safe cracking
    • Packing material from safe 

    • Most crimes – many specialists
    • E.G. Home invasion
    • Ident (the REAL CSI!) - scene
    • Pathologist - body
    • Biology – DNA, semen
    • Firearms – spent cartridges
    • Chemist – all aspects!
  5. Chemists involvement
    • Fibres left behind
    • Soil from assailant’s shoes
    • Glass on suspects clothes
    • Rope used to tie homeowners
    • Strange stain on floor (gasoline?)
  6. Analysis (Chemist)
    • Ø Substance could be anything!Ø Broad range of tests to determine constituentsØ First tests – gasolineØ Further tests – type of gasoline – Esso
    • Further tests – batch of Esso gas
    • Qualitative analysis – what substances are present
    • Quantitative analysis  - % of each
  7. Techniques of analysis (chemistry)
    • Basic chemistry techniques
    • Chromatography
    • Electrophoresis
    • Spectrophotometry
  8. Chromatography
    • Separates substance into components (so purifies them)
    • Gas Chromatography – separates based on distribution between liquid and gas phase
    • Gas chromatograph (GC) - inject sample
    • Pyrolysis – adds heat, e.g. paint chip-gas
    • High-Performance Liquid Chromatography (HPLC)
    • Thin-layer Chromatography (TLC)
  9. Electrophoresis
    Separates substances on basis of electrical potential
  10. Spectrophotometry
    • Different substances absorb light in different ways
    • Used to identify
    • Mass Spectrometry (MS)
    • Gas chromatography – tentative ID
    • GC +MS (GC/MS) – positive ID
    • Very basic techniques, first year chemistry
  11. Significance
    • Identifying substance  - basic chemistry
    • Significance of substance – FORENSiC chemistry
    • Class evidence
    • In order to have value  - must determine significance
    • May have 0 significance
    • May be very significant
  12. Significance
    • Class evidence – may be high or low significance
    • Exact match? But may be very common – so exact match to many different items
    • If rare – more significant
    • How common is evidence?
    • Need databases for comparison
  13. Determining Significance 1.
    • How common is this evidence?
    • Develop database – parent population
    • E.g. B & E, glass at scene
    • Suspect has glass on him
    • Physical properties – do they match?
    • How common is that sort of glass?
    • If common, does it mean anything? Determining Signif. 1 contd.
    • Glass on person?
    • Develop a database
    • How common is it for regular people to have glass on them?
    • Get a sample of people
    • See how much glass on them
    • Shoes - ~30%
    • Clothes ~<2%
    • So: -
    • Glass itself is common
    • But rare to have glass on clothing
    • So, significant that suspect had matching glass on clothing
    • <2% population have any glass
    • Even more significant that it is that type of glass
    • Less significant if just on shoes (position on shoes?)
  14. Determining Significance 2
    • How valid is your database?
    • Does it fit this person – or how likely is it that this person could innocently have this evidence?
    • Glass on clothing rare – but what if guy is a glazer?
    • Suspect must fit in research population

    • Validity:
    • Drywall?
    • Rare in average populationØ
    • Not in person renovating
    • Gun residue?
    • Rare in average population
    • Not in person at gun range
    • Therefore, need database into which suspect fits
    • How common is it to find glass on glazier’s clothes?
  15. Determining Significance 3
    • What is population/situation?
    • Some things may be very common in some situations and very rare in others
    • Livingston in Africa
    • Scenario?
    • Manure from bomb?
  16. Determining Significance 4
    • More than one type of class evidence
    • Cumulative - the more there is the more significant – multiplies probabilities
  17. Fibres
    • Natural fibres – animal or plant sourcesØ Manmade fibers
    • Polymers –
    • e.g. nylon  (large number of atoms)also include paint, adhesives, plastics
  18. Fibre examination
    • Colour
    • Striations on fibre
    • Cross-sectional shape
    • Refractive index
    • Infrared spectrophotometry
    • Etc.
    • How rare is the fibre? Circumstances?
  19. Significance/circumstances (fibre)
    • Hit and Run
    • Fuzzy sweater fibres
    • Very common
    • BUT – not common stuck in broken head light glass of a car with a smashed fender
    • Glass from light on victim?
    • Exchange of evidence – very significant
  20. Paint
    • Everywhere!
    • Cars – all have at least 4 layers normally
    • Match to database of car colours
    • Chemically examine paint – e.g. chromatography
    • If repaint job – more significant but harder to find
    • Car brake lights – on or off?
  21. Arson
    • Chemist may attend AND may be special fire investigators
    • May be direct arson for the sake of the fire
    • May be insurance
    • May be to disguise a crime
    • Very difficult to destroy a body!
    • Usually lots of evidence left behind!
    • Remember – body in dumpster? 
    • Arson?
    • Was it arson?
    • Accelerant?
    • Gas?
    • Chemicals?
    • Kindling?
    • “bounce”?
    • Significance?
    • Where is it found?

    • Samples
    • Collect Sample
    • Must take a control
    • If an accelerant is found, is it also on control?
    • Then maybe not used as an accelerant
    • Many accelerants can be specifically identified
  22. Explosions, bombs
    • Usually homemade
    • How was it constructed?
    • What was it made of?
    • What explosive was used?
  23. Explosion
    • Combustion with release of gases, which expand with the heat
    • Very fast
    • If confined – pipe bomb – shrapnel
    • Large blast – gases escape - >7000mph
    • Gale force – knocks over buildings, walls, kills
  24. Classification of explosives
    • Based on speed at which the explosive decomposes
    • Low explosives – speed of deflagration (burning) – rapid oxidation, heat, light, subsonic pressure wave.
    • High explosives – speed of detonation – creation of supersonic shock wave – instantaneous build up of heat and gases
  25. Low explosives
    • Throwing or propelling motion
    • Normally just burn
    • Black powder, smokeless powder
    • e.g. fuse to gunpowder
    • Lethal when confined  - pipe bomb
  26. High Explosives
    • Primary explosives – ultra-sensitive to heat, shock or friction. Detonate violently instead of burn. Primers, blasting caps
    • Secondary explosives – insensitive to heat, shock or friction. Burn rather than detonate if in open air e.g. dynamite, TNT etc.
    • Bombs must be detonated by an initiating explosion
  27. Bombs
    • Explosive
    • Timers
    • Detonators
    • Fuses
    • Batteries?
    • Duct tape?
Author
ID
318899
Card Set
CRIM 355
Description
Forensic chemistry
Updated
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