Crime Scene

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Crime Scene
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• Essential Question
• Content Objective
• Language Objective

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Crime scene

• 1st on scene
• 1st priority people safety
• 2nd priority secure the scene keep people from
  altering evidence
• 3rd priority detain suspects/witnesses

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Questions

• ASAP as soon as possible
• Question 1st on scene and witnesses about any
  transient evidence
• Weather, odors, visibility, pts. Of entry/exit

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Crime scene process

• 1 Safety
• 2 Secure the scene
• 3 Preliminary survey (boundaries, exits)
• Narative, photograph, sketch
• 4 Detailed search
• Narative, photograph, sketch
• 5 Record/collect data
• 6 Final survey release crime scene

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Preliminary Survey

• From outside the crime scene do not know
  boundaries of crime scene
• body may have been dragged
• drugs may have been dropped while fleeing the
  scene

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Preliminary Survey

• Narrative
• detailed and legible
• Time line
• Measure scene and note locations
• Describe time of day, weather, lighting
• Written description of physical evidence
• Names of people involved

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Preliminary Survey

• Photograph
• Before touch or move anything
• Take photos from different angles
• Have ruler for scale
• Photo from outside to inside in order
• Photograph each piece of evidence individually-
  and from far away

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Preliminary Survey

• Sketch key - scale - compass
• Original sketch is evidence in case
• Measurement to scale - relative locations
• Scale gives relationship of sketch to actual
  size
• Key explains code used in sketch
• Compass for orientation

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Detailed survey

• From within the crime scene
• Photograph
• Sketch
• Narrative
• Collect evidence
• Initiate chain of custody

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• Chain of custody a list of all persons who came
  into possession of an item of evidence
•  

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Custody

• Samples and data are considered to be in your
  custody when
• they are in your physical possession
• they are in your view, after being in your
  physical possession
• they are in your physical possession and then
  locked up so that tampering cannot occur
• they are kept in a secured area, with access
  restricted to authorized personnel only.? 

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Chain of custody

• Keep the number of people involved in collecting
  and handling samples and data to a minimum.
• Only allow people associated with the project to
  handle samples and data
• Always document the transfer of samples and data
  from one person to another on chain-of-custody
  forms
• Always accompany samples and data with their
  chain-of-custody forms.

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Control

• Control physical evidence whose origin is known
  (exemplar), such as blood or hair from a suspect
  that can be compared to crime-scene evidence
•   Buccal swab swab of inner portion of cheek
  cheek cells are usually collected to determine
  the DNA profile of an individual

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Collection of evidence

• Wet items dry them, package them to prevent
  molding
• Biological items freeze them.
• Fire arms fixed inside wooden container
• Fumes (arson) kept in airtight container
• Collect most delicate items first (transient
  evidence)

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Physical Evidence

• Types of physical evidence encountered at crime
  scenes.
• Difference between the identification and
  comparison of physical evidence.
• Physical evidence possessing individual and class
  characteristics.
• Value of class evidence to a criminal
  investigation

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• Identification the process of determining a
  substances physical or chemical identity
• Comparison the process of ascertaining whether
  two or more objects have a common origin
• Individual characteristics properties of
  evidence that can be attributed to a unique
  source with an extremely high degree of certainty

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• Class characteristics properties of evidence
  that can only be associated with a group and
  never with a single source
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• Reconstruction the method used to support a
  likely sequence of events by the observation and
  evaluation of physical evidence, as well as
  statements made by those involved with the
  incident
•  

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The Role of Forensic Science

• Provide scientific information to the legal
  community
• Done via reports and testimony
• A statement of the limitations on conclusions
  drawn from an experimental result is an essential
  element

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Responsibility of the Analyst

• May conclude that an evidence object a
  reference object show similar traits
• Must understand and communicate the limitations
  inherent in the conclusion
• limitations are a combined function of
• the nature of the traits
• the sensitivity and resolution of the detection
  methods
• the state of the evidence

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Legal vs. Scientific Questions

• The law must establish that a crime has been
  committed by defining the corpus delecti (body of
  the crime)
• All elements that legally define any particular
  crime must be present to proceed
• The forensic scientist must translate the legal
  question into a scientific question

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Thinking Forensically

• A cognitive framework for a forensic investigation

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Fundamental Principles

• Transfer
• Locard Exchange Principle
• Identification
• placing objects in a class
• Individualization
• narrowing the class to one

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The Locard Exchange Principle

• Every time an object comes into contact with
  another object, it either leaves a portion of
  itself or takes a portion of the other object
  with it
• Every contact leaves its trace

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Transfer

• Physical movement of material from one place to
  another
• 1 mm fiber transferred from a sweater (its
  source) to a sweatshirt (its destination) during
  contact

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Transfer

• No physical movement of material
• a pattern formed when an object makes an
  impression on some receptive substrate
• shoe stepping in mud (no detectable amount of
  leather left by shoe

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Identification by Class Characteristics

• Classes of objects can be progressively narrowed
  by looking at successively more traits
• Results in continually fewer objects being
  classified as similar to each other
• If the traits being compared are not unique to
  the source
• item will possess traits that might be shared
  with a wide variety of sources

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• Once an object is identified by class, the object
  can be compared to a reference (known) item
• determine if it came from that source or some
  other

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Individualization

• Individualization answers the forensic
  investigation questions
• Which one is it? (animate items)
• Whose is it? (inanimate items)
• Accomplished by examining traits that are unique
  to a source item
• any progeny can only have originated from that
  particular source item

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Individualizing Traits

• Minutiae of friction ridges on fingers
  (fingerprints)
• nicks, cuts or gouges in a tire
• fine striae in the barrel of a firearm
• DNA markers

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Individualizing Characteristics

• If two objects possess individualizing
  characteristics so that the analyst can conclude
  that no other items exhibit this array of traits
• association is absolute
• analyst concludes that the items share a common
  origin with each other
• latent print at crime scene and a reference set
  of prints made at the police station