friday, september 9, 2011
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Friday, September 9, 2011. How does new evidence affect what you think happened in a crime?. G o S t o w ! B e a t F i r e s t o n e !. - PowerPoint PPT PresentationTRANSCRIPT
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Friday, September 9, 2011
How does new evidence affect what you think happened in a
crime?
Go Stow!
Beat Firestone!
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Chapter 2
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Ch. 2 Crime Scene Investigation and Evidence Collection
By the end of this Chapter you will be able to:
Summarize Locard’s exchange principle Identify four examples of trace evidence Distinguish between direct and circumstantial evidence Identify the type of professionals who are present at a crime sceneDescribe how evidence from a crime scene is analyzed
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Summarize the three steps of a crime scene investigation Explain the importance of securing the crime scene Identify the methods by which a crime scene is documented Demonstrate proper technique in collecting and packaging trace evidence
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To recognize, document, and collect evidence at the scene of a crime.
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What is a crime?Crime – An offense against the public at large, proclaimed in a law and punishable by a governing body.
Criminal Law – The body of law that, for the purpose of preventing harm to society defines what behavior is criminal and prescribes the punishment to be imposed for such behavior
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Court Roles
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Classification of CrimesFelony – A relatively serious criminal offense punishable by death or imprisonment for more than a year in a state or federal prison
Misdemeanor – A less serious crime that is generally punishable by a prison sentence of not more than one year in a county or city jail
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Criminal InvestigationThe lawful search for people and things to reconstruct the circumstances of an illegal act, apprehend or determine the guilty party, and aid in the state’s prosecution of the offender(s).
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Deductive vs. Inductive Reasoning
• Deductive Reasoning:• The drawing of
conclusions from logically related events or observations
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Deductive vs. Inductive Reasoning
• Inductive Reasoning:• The making of
inferences from apparently separate observations or pieces of evidence.
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•Formulate Formulate a question worthy of investigation.
•Formulate a reasonablereasonable hypothesis to answer the question.
•TestTest the hypothesis through experimentationexperimentation..
•Upon validation of the hypothesis, it becomes suitable as scientific evidence.evidence.
The Scientific Method
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When a person comes in contact with an object or another person, material can be transferred.
More intense interactions result in greater exchange.
Transferred material is known as trace evidence.
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Direct evidence – Firsthand observationsExamples: eyewitness accounts, video, etc.
Circumstantial evidence – Indirect physical or biological evidence that can link a person to a crime, but don’t directly prove guilt.Physical examples: bullets, weapons, fibers, tool
marks, etc.Biological examples: body fluids, hair, plant parts,
etc.
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Explain why this would be or
would not be trace evidence
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Class evidence – narrows an identity to a group of persons or things.Example: Paint chip from a blue 1987
Toyota.
Individual evidence – narrows an identity to a single person.Example: DNA sample
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Bell Work: 9/11/13
What is Locard’s Exchange Principle?
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Who is at the crime scene?
Police and …
District attorney (possibly)
Crime scene investigators
Medical examiners
Detectives
Specialists
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1. Securing the Scene Responsibility of the first responder Restricts entrance to scene Starts log of all persons entering May send for additional experts or officers
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2. Separate and question the witnesses When did the crime occur? Who called it in? Who is the victim? Can the perpetrator be identified? What did you see happen? Where were you when you observed the
crime scene?
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3. Scanning the Scene Determine where photos should be taken Determine if the location is a primary
crime scene (where the crime occurred), or a secondary location (such as where a body was moved).
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4. Seeing the Scene Take photos, including close-up pictures
with and without rulers for scale.
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5. Sketching the Scene Drawn to scale All objects should be measured from two
immovable objects Direction of North should be included Scale of drawing, date, and location
should be included.
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6. Searching for Evidence-Tools such as flashlights, UV lights, or vacuums may be used.Investigators walk patterns to avoid missing anything
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Search Patterns
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7. Securing and Collecting Evidence –Liquids and arson remains are stored
in airtight, unbreakable containers.
Biological evidence is placed in a breathable container to dry.
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After drying, biological evidence is transferred to a paper bindle and sealed in a bag.
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Packaging the Evidence1. Crease a clean paper and
place evidence in the X position
2. Fold in the left and right sides, and then fold in the top and bottom
3. Put the bindle into a plastic or paper evidence bag affixing a seal over the opening
4. Write your name on the seal
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Each different item or similar items collected at different locations must be placed in separate containers. Packaging evidence separately prevents damage through contact and prevents cross-contamination.
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Chain of Custody—A list of all persons who came into possession of an item of evidence.
Continuity of possession, or the chain of custody, must be established whenever evidence is presented in court as an exhibit.
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This means that every person who handled or examined the evidence and where it is at all times must be accounted for. Maintaining a chain of custody log is essential to present credible evidence in court
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1. Bag the evidenceAdd identification Seal itSign it across the sealed edge
2. Sign over to a lab technician Open bag on non-sealed edge
3. Return items to the evidence bagSeal evidence bag in another bagSign the evidence log
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Evidence ID Forms
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After a crime-scene investigation, forensic lab work begins.
Test results lead to a crime scene reconstruction.
Test results can be used to identify staged crime scenes.
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Facts result from collected evidence processed by the forensic lab
Lead detective aims to see how facts fit into the crime scenario
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Lab results can: Lab results can:
Show reliability of witness accounts
Establish the identity of suspects or victims
Show suspects to be innocent or link them with a scene or victim
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Crime SceneCrime Scene Reconstruction Reconstruction
Crime scene reconstruction involves:
Forming a hypothesis of the sequence of events from before the crime was committed through its commission
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Staged Crime Scenes
When lab results don’t match up with the testimony of witnesses
Common examples:
Staging a fire—to cover bankruptcy
Staging a suicide—to cover a murder
Staging a burglary—to collect insurance money
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Was the crime scene staged? Consider:
Does the type of wound match the weapon?
Could the wound be easily self-inflicted?
What were the mood and actions of the victim before the event?
What were the mood and actions of the suspect before the event?