Introduction to Forensic Science
Specialists
Forensic Medicine (M.D) Forensic Science (BS / BSc)
DNA
Drugs
Ballistics
The Body (Living & Dead)
Physical Evidence
Documents
Fingerprinting
How did they know?
o Interpretation of Evidence
Found at Crime Scene
Physical objects or Measurement
o Reliability of Evidence
How evidence can be trusted
To what extent can it be trusted
DNA is very reliable
o Can be deduced vs Cannot be deduced from evidence
Some aspects beyond the power of forensic science
Limits
Convince Judge or Jury of the validity of the forensic evidence
In court, have to show
1. criminal action was committed (Actus Reus)
2. intention to commit the criminal action (Mens Rea)
, Limits of Forensic Science
o Tells you about Actus Reus but not Mens Rea
o “Actus non facit reum nisis mens sit rea” The act does not
make a person guilty unless the mind is also guilty
Locard’s Exchange Principle
o “Only human failure to find it, study and understand it, can
diminish its value.”
o Every contact leaves a trace
Toxicology Drugs and Poisons in body fluids and organs
Polygraph “Lie Detector”
Computer Forensics Data
Forensic Engineering Structures
Entomology Using insects to provide info
Forensic Geology Soil Analysis
Anthropology Analysis of skeletal remains
Facial Reconstruction Take skull & rebuild flesh
o See how person looked like when they were alive
Forensic Odontology Using teeth to provide information
o Identification of victims remains
o Identification of criminal
Identification & Individualization
Reconstruction & Re-enactment
2
,Chemical Analysis in Forensic Science
Identification what it is made of (Spectroscopy)
o Elemental analysis to give required information
o Eg. Poisoning, time of death, bullets
Elements
o Cannot be broken down (by chemical means)
o Can neither be created nor destroyed
o Bullets’ bulk composition is Pb, but there are also trace
impurities
o Studying these trace impurities will identify where that bullet
came from since it differs from bullet to bullet
Analysis of Elements: Bulk composition + trace impurities
o Trace impurities more informative for forensic scientists
Chemical tests (not useful now technology)
o Disadvantages Large amounts of samples required,
destructive (destroying evidences), subject to interference
(analysis of one element may interfere another element)
o Advantages fast, easy to do, simple equipment (test-tubes)
ppm part per million, ppb part per billion
Structure of the Atom
o Electrons restricted to specific energy levels energy is
quantized and not continuous
o Can move from one level to another
3
, o Absorbed/release energy in the form of EM radiation/light
must match amount of energy released (no energy loss?)
o Absorption spectroscopy (for elements) radiation is only
absorbed when the frequency of light matches the difference
between the energy levels
o Electron promoted to higher energy level excited state
o Emission spectroscopy most frequencies of radiation are not
emitted as they do not match the difference between the energy
levels as electrons drop from one energy level to a lower energy
level, only specific frequencies.
o When this light is emitted into a prism, we obtain a pattern that
is mostly black but with certain colored lines that match the
energy difference
o Pattern is characteristic for each element
o Flame test Metal salt added to flame color produced
energy of flame excites electrons these electrons drop back
to ground state emit coloured light different metal
different color because of the varying energy difference
Elemental Analysis
o Neutron Activation Analysis (NAA)
o irradiate sample with neutrons hit nucleus nucleus is
excited (compound nucleus) decays give out gamma ray
ends as a product nucleus
o Gamma rays are characteristic: Measure energy of gamma ray
and analyze element
o Advantage: Non-destructive Sample
o Disadvantage: Requires nuclear reactor
Analysis of Microscopic Objects
o Eg. Gunshot Residue Particle (GSR particle)
4
Specialists
Forensic Medicine (M.D) Forensic Science (BS / BSc)
DNA
Drugs
Ballistics
The Body (Living & Dead)
Physical Evidence
Documents
Fingerprinting
How did they know?
o Interpretation of Evidence
Found at Crime Scene
Physical objects or Measurement
o Reliability of Evidence
How evidence can be trusted
To what extent can it be trusted
DNA is very reliable
o Can be deduced vs Cannot be deduced from evidence
Some aspects beyond the power of forensic science
Limits
Convince Judge or Jury of the validity of the forensic evidence
In court, have to show
1. criminal action was committed (Actus Reus)
2. intention to commit the criminal action (Mens Rea)
, Limits of Forensic Science
o Tells you about Actus Reus but not Mens Rea
o “Actus non facit reum nisis mens sit rea” The act does not
make a person guilty unless the mind is also guilty
Locard’s Exchange Principle
o “Only human failure to find it, study and understand it, can
diminish its value.”
o Every contact leaves a trace
Toxicology Drugs and Poisons in body fluids and organs
Polygraph “Lie Detector”
Computer Forensics Data
Forensic Engineering Structures
Entomology Using insects to provide info
Forensic Geology Soil Analysis
Anthropology Analysis of skeletal remains
Facial Reconstruction Take skull & rebuild flesh
o See how person looked like when they were alive
Forensic Odontology Using teeth to provide information
o Identification of victims remains
o Identification of criminal
Identification & Individualization
Reconstruction & Re-enactment
2
,Chemical Analysis in Forensic Science
Identification what it is made of (Spectroscopy)
o Elemental analysis to give required information
o Eg. Poisoning, time of death, bullets
Elements
o Cannot be broken down (by chemical means)
o Can neither be created nor destroyed
o Bullets’ bulk composition is Pb, but there are also trace
impurities
o Studying these trace impurities will identify where that bullet
came from since it differs from bullet to bullet
Analysis of Elements: Bulk composition + trace impurities
o Trace impurities more informative for forensic scientists
Chemical tests (not useful now technology)
o Disadvantages Large amounts of samples required,
destructive (destroying evidences), subject to interference
(analysis of one element may interfere another element)
o Advantages fast, easy to do, simple equipment (test-tubes)
ppm part per million, ppb part per billion
Structure of the Atom
o Electrons restricted to specific energy levels energy is
quantized and not continuous
o Can move from one level to another
3
, o Absorbed/release energy in the form of EM radiation/light
must match amount of energy released (no energy loss?)
o Absorption spectroscopy (for elements) radiation is only
absorbed when the frequency of light matches the difference
between the energy levels
o Electron promoted to higher energy level excited state
o Emission spectroscopy most frequencies of radiation are not
emitted as they do not match the difference between the energy
levels as electrons drop from one energy level to a lower energy
level, only specific frequencies.
o When this light is emitted into a prism, we obtain a pattern that
is mostly black but with certain colored lines that match the
energy difference
o Pattern is characteristic for each element
o Flame test Metal salt added to flame color produced
energy of flame excites electrons these electrons drop back
to ground state emit coloured light different metal
different color because of the varying energy difference
Elemental Analysis
o Neutron Activation Analysis (NAA)
o irradiate sample with neutrons hit nucleus nucleus is
excited (compound nucleus) decays give out gamma ray
ends as a product nucleus
o Gamma rays are characteristic: Measure energy of gamma ray
and analyze element
o Advantage: Non-destructive Sample
o Disadvantage: Requires nuclear reactor
Analysis of Microscopic Objects
o Eg. Gunshot Residue Particle (GSR particle)
4
