Honors Forensic Science. Crime Labs “run” on physical evidence Physical Evidence = any and all...
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Transcript of Honors Forensic Science. Crime Labs “run” on physical evidence Physical Evidence = any and all...
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The Crime SceneHonors Forensic Science
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I. Processing the Crime Scene
Crime Labs “run” on physical evidence
Physical Evidence = any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator
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To be effective, evidence must be:
Recognized Collected and processed properly
Collector must be selective using knowledge of crime lab techniques, capabilities and limitations
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Crime labs do not solve crimes
Many jurisdictions have specialized teams to conduct crime-scene searches
Not all crime scenes require retrieval of physical evidence
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II. Secure and Isolate Crime Scene
First officer(s) on scene should:
Provide medical assistance, if needed, to victims
Arrest perpetrator if present Preserve and protect area as much as
possible
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II. Cont’ d
Exclude all unauthorized personnel from scene
Isolate area using ropes, tape, barricades, guards, etc.
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Lead Investigator should:
Determine boundaries Determine perp’s path of entry and exit Document obvious items Conduct initial walk-through Develop examination strategy
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Record the Scene
Must document the crime scene in original state
Information used in investigation and in court
Monetary limitations may determine method used to document the scene
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Photography Must be in unaltered condition Crime scene photographed completely Items of physical evidence
photographed to show position and location; close-ups to show detail
If size is important, include a measurement scale in photo for reference
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Videography Can be used to augment photography Can narrate events on videotape Does not replace photography
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Sketches
Rough Sketch
Containing an accurate depiction of the dimensions of the scene and showing the location of all objects having a bearing on the case
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Rough sketch should include; Recovered items of physical evidence Distance measurements of items (use 2
fixed points) Legend Compass heading designating north
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Finished Sketch
A precise rendering of the crime scene, usually drawn to scale
Often prepared with aid of templates and drafting tools
Reflect same information as rough draft
CAD programs often used
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Notes
Must be a constant activity Should include detailed written
description of scene Detailed description of evidence:
location of items, time item discovered, by whom, how and by whom it was packaged, etc.
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Notes often only written record of details
Tape-recording can be advantageous, but still should be transcribed into a written document
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Conduct Systematic Search
Thorough and systematic, even if seems unnecessary at the time
How crime scene is searched depends on type of crime, local and size of scene, # of collectors, etc.
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Collect massive objects to microscopic traces
Important to collect possible carriers of trace evidence as well as obvious items
Portable vacuum cleaners helpful
Medical examiner may also provide evidence
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Medical examiner may collect and forward: Victim’s clothing Fingernail scrapings Head and pubic hairs Blood (for DNA typing) Vaginal, anal, and oral swabs Recovered bullets from body Hand swabs from shooting victims
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Collect and Package Physical Evidence
Prevent change
Change can arise from contamination, breakage, evaporation, accidental scratching or bending, or loss through improper or careless packaging
Maintain evidence in original condition if possible
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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 prevent contamination
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Maintain Chain of Custody
Chain of custody – list of all persons who came into possession of an item of evidence
Must be established whenever evidence is presented in court
Adhere to standard procedures Keep to a minimum
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Obtain Controls
Examination of evidence often requires comparison with known standard or control
Control = physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared to crime scene evidence
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Quality and quantity of controls may help determine evidential value of crime-scene evidence
Controls must be treated with equal care as actual evidence
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Submit Evidence to Lab
Usually submitted personally or by mail shipment
Must be accompanied by evidence submission forms
List of tests to be performed on each item
List of items submitted
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Crime Scene Safety
International Association for Identification Safety Committee Gloves Particle masks/respirator, goggles, face
shield Be alert to sharp objects Use biohazard bags Note taking done with uncontaminated
gloves No eating, drinking, smoking, etc. at
crime scenes
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Legal Considerations
Fourth Amendment – Prohibits unreasonable search and seizure
Mincey v. Arizona Michigan v. Tyler When time and circumstances
permit, obtain a search warrant before investigating and retrieving physical evidence at crime scene