Investigating a Crime

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Investigating a Crime

• CLU3M

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Collecting Physical Evidence

• When a crime has been committed, the first job of
  the police is to collect all the evidence that
  they can find
• The careful collection, examination, and storage
  of physical evidence are a vital part of any
  criminal investigation.

• To protect the crime scene, the officers must
  accurately establish two boundaries
• The centre the area in which the offence was
  actually committed
• The perimeter the areas surrounding the centre,
  where the offender may have been present or may
  have left evidence

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Crime scenes are preserved for 3 reasons

• To allow for a thorough search of the crime
  scene.
• To seize and collect physical evidence.
• To ensure that the physical evidence is
  admissible in court.
• Contamination the loss, destruction, or
  alteration of physical evidence

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Forensic Science

• Forensic science is the use of biochemical and
  other techniques to analyze evidence
• It involves many different disciplines including
  alcohol, anthropology, chemistry, document
  identification and forgery, entomology,
  fingerprints, firearms, trace evidence,
  odontology, biology and pathology

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Forensic Science

• A piece of evidence found at the scene of a crime
  will often be analyzed by several different
  methods to get the most information from it.
• I.e., a shoe may be examined for bloodstains
  (studied by biology, DNA analysis), trace
  evidence (broken glass or similar type of dirt
  found on suspects shoe and crime scene), gunshot
  residue (may be on suspect's clothes or hands as
  well) etc.

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Impressions

• Patterns or marks found on surfaces and caused by
  various objects such as figures, shoes, tires,
  blunt objects, etc

• Impressions have 2 characteristics
• Class characteristics the general attributes of
  the object i.e. type of tire (Pirelli 15 inch
  radial)
• Individual characteristics specific and unique
  of an object i.e. tread wear on a specific tire

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Fingerprints

• The unique patterned mark left behind after a
  fingertip touches an object
• It is unique to an individual and never change

• There are 2 types of prints
• Visible fingerprint can be observed by the naked
  eye i.e. coated in blood or grease
• Latent fingerprint formed by natural oils and
  perspiration on the fingertip. Not visible to the
  naked eye.

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Three methods are used to develop latent prints

1. Graphite powder used on non-absorbent surfaces
   i.e. metal plastic
2. Iodine fuming used on surfaces such as paper and
   cloth
3. Laser beam used to illuminate the print

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DNA Testing

• DNA (Deoxyribonucleic Acid) - is the individual
  blueprint of a human being at a genetic level
• This is the newest of forensic science methods,
  as it was only developed in the 1980s.
• It is a very reliable way of linking an accused
  person to a crime..
• can be found in the form of blood, seminal fluid,
  saliva, or skin.
• Once a person's DNA has been identified as the
  same as that found at a crime scene, there is a
  tiny chance that that person was not present, as
  only an identical twin would have exactly the
  same DNA.

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Forensic Ballistics

• the science of analyzing firearm usage in crimes.
• Forensic ballistics involves analysis of bullets
  and bullet impacts to determine the type of
  firearm used.
• firearm and tool mark examinations also involve
  analyzing firearm, ammunition, and tool mark
  evidence in order to establish whether a certain
  firearm or tool was used in the commission of a
  crime.

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The Crime Scene Continued

• There are strict procedures on the seizure,
  handling, and storage of evidence
• no evidence is left unattended
• the case officer must secure evidence in the
  police property locker
• transferring evidence is the responsibility of
  the case officer
• no evidence can be removed from property locker
  without appropriate authority and signature. This
  is to maintain the chain of custody of the
  evidence.