P1254325929xUoQX - PowerPoint PPT Presentation

Title: P1254325929xUoQX


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Crime Lab Investigation
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Forensic Detectives
Hollywood vs. the Real Forensic Detectives
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1 Task

• Determine if there is physical evidence that
  connects the suspect to the crime.
• Is there evidence that places the suspect at the
  crime scene? If so...
• Is there evidence that shows the suspect actually
  committed a crime at the crime scene?

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Approach

• Take advantage of the fact that there is always
  some exchange of physical evidence between
  criminal and the crime scene
• Either criminal leaves something at the crime
  scene that can be connected to him/her...
• Or criminal picks up something at the crime scene
  that connects him/her to the scene.

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Evidence Collection

• Forensic scientists (also called criminalists) do
  not normally go into the field to collect
  evidence except for high profile cases.
• They normally train detectives and police
  officers to perform the task of evidence
  collection.

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Evidence Examination

• The physical match is the strongest form of
  evidence.
• It is strong because of the certainty of
  connecting suspect to crime scene.
• In the court it is more convincing because of the
  obvious visible match.

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Evidence Examination

• If a physical match is not possible, do
  comparisons.
• Use equipment that makes comparisons easier.

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Click on image to see split screen of two
casings.
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Evidence Examination

• When identification is needed, screen first, then
  identify.

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Heroin
Amphetamine
Marquis Reagent
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Duquenois-Levine Reagent
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HIGH PRESSURE
LIQUID CHROMATOGRAPHY
CHROMATOGRAPHY
WRITE
COLOR
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Thin Layer Chromatography (TLC)
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GAS CHROMATOGRAPHY
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GAS CHROMATOGRAPH
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Blood Samples from DUI Cases
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Gas Chromatograph - Mass Spectrometer
GC-Mass Spec
Separates (purifies) the different compounds from
a mixture. Can give a positive identification or
at least a strong indication of a substances
identity.
Measures the Mass (formula weight/molecular
weight) of the substance, which completes the
identification.
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Automation
For CourtroomCredibility
Faster testing
More reliable testing

1. Run a known standard
2. Run a blank
3. Run the unknown

For comparison purposes
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Documentation is Critical
Computer skills are needed Keyboarding skills are
needed
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Automation
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High volume
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Fast testing
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Automation
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PCR Thermal Cycler

• The Polymerase Chain Reaction (PCR) is a
  technique where a sequence DNA can be amplified
  (duplicated) a billion fold in just hours.
• Minute samples of DNA isolated from blood at a
  crime scene can be used to determine if an
  individual was actually at the location of the
  crime.

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Visualization Techniques
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Forensic Detectives
Hollywood vs. the Real Forensic Detectives
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Pictures and animations byKen Costello
Pictures and animations byKen Costello