Chapter 2 the crime scene
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Chapter 2 The Crime Scene. Processing the Crime Scene. Forensic Science begins at the crime scene Investigators must recognize physical evidence, collect the evidence, and properly store and preserve the evidence

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Chapter 2 the crime scene

Chapter 2The Crime Scene


Processing the crime scene
Processing the Crime Scene

  • Forensic Science begins at the crime scene

  • Investigators must recognizephysical evidence, collectthe evidence, and properly store and preservethe 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


Processing a crime scene
Processing a Crime Scene

  • Secure and isolate the crime scene

  • Record the scene

  • Conduct a systemic search for evidence

  • Collect and package physical evidence

  • Maintain a chain of custody

  • Obtain standard/reference samples

  • Submit evidence to the laboratory


Secure and isolate the crime scene
Secure and Isolate the Crime Scene

  • Responsibility of first officer to arrive on the scene of a crime to preserve and protect the area to the greatest extent possible

  • First priority is to obtain medical assistance and arrest perpetrator

  • Next, efforts should be made to exclude all unauthorized personnel and isolate area; every person that enters the scene has potential to destroy evidence

  • Determine boundaries and establish the perpetrator’s path of entry and exit; crime scene size will depend of locale of scene, size of area, and victims and suspects


Record the scene
Record the Scene

  • There is a limited amount of time to permanently record the crime scene in its untouched state

  • Recording the scene is necessary to present in trial and delineate the location of evidence

  • Three methods of recording a crime scene:

    • Photography

    • Sketches

    • Notes


Record the crime scene
Record the Crime Scene

  • Photography

    • Unless there are injured parties, objects must not be moved until they have been photographed from all angles. If objects are moved, photographs may not be admissible in court – unless recorded in notes.

    • Items to be photographed:

      • Area in which the crime took place and all adjacent areas

      • Points of entry and exit from various angles

      • If indoors, the entire room and wall area as well as adjacent rooms

      • A body’s position and close up depicting injuries and near by weapons; once the body is removed, the area under the body should be photographed

      • Physical evidence position and location as well close up (a ruler or other measuring devise may be used as a point of reference)

  • Videotaping with sound is also a popular method of recording a crime scene


Record the scene1
Record the Scene

  • Sketches

    • Rough sketch of the dimensions of the scene showing the location of al objects

    • The dimensions of objects in the sketch are determined by two fixed point – usually the walls of the room

    • Finished sketches are usually completed with drafting tools (CAD)


Record the scene2
Record the Scene

  • Notes

    • Detailed written description of the scene with location of items of physical evidence

    • Time of discovery of evidence, by whom, how and by whom it was packaged and marked, and the disposition of the item after it was collected

    • Notes may be the only written record to refresh the memory of the investigators

    • Tape-recording is commonly done


Conduct a systematic search for evidence
Conduct a Systematic Search for Evidence

  • Searching the crime scene depends on locale and size of area as well as victims and suspects

  • Lead investigator will subdivide the scene into segments a search each segment individually or the search may start at some outer point and gradually move toward the center of the scene in a circular fashion


Conduct a systematic search for evidence1
Conduct a Systematic Search for Evidence

  • Areas searched must include all probable points of entry and exit

  • Search for evidence will depend on type of crime:

    • Homicide

    • Burglary

    • Vehicular

    • Kidnapping

  • Physical evidence can be anything from massive objects to microscopic traces

  • Some objects may only be traceable in laboratory settings therefore the collection of possible carriers of trace evidence is important

    • Minute traces of blood on clothing

    • Hair or fibers in vacuum sweepings


Conduct a systematic search
Conduct a Systematic Search

  • The search for evidence continues in the autopsy of a deceased victim

  • Medical examiner will determine cause and manner of death and will retain tissues and organs for toxicological and pathological testing

  • The following should be collected and sent to the forensic lab:

    • Victim’s clothing

    • Fingernail scrapings

    • Head and pubic hair

    • Blood

    • Vaginal, anal and oral swabs (in sex related crimes)

    • Recovered bullets from the body

    • Hand swabs from shooting victims (gunshot residue)


Collect and package physical evidence
Collect and Package Physical Evidence

  • Physical evidence must be handled and processed in a way that prevents any change from the crime scene and the time it is received by the crime laboratory

  • Changes arise through contamination, breakage, evaporation, accidental scratching or bending, or loss through improper or careless packaging

  • Whenever possible, evidence should be submitted to the lab intact; blood, hairs, fibers, soil particles should not be removed from articles

  • Each different item or similar items collected at different locations must be placed in separate containers to prevent damage and cross-contamination.


Examples of packaging containers and techniques
Examples of packaging containers and techniques:

  • Plastic pill bottles for hairs, glass, fibers, and other types of small evidence

  • Manila envelopes or screw-top glass vials for trace evidence (never ordinary envelopes because of possible leaking)

  • To avoid accumulation of moisture and mold, bloodstained materials should be packaged in manila envelopes or paper bags

  • Clothing should be air dried and placed in paper bags to allow air flow

  • Charred debris should be sealed in an airtight container to prevent evaporation

  • See Appendix I for proper collection and packaging techniques


Maintain chain of custody
Maintain Chain of Custody

  • Chain of custody – continuity of possession must be established whenever evidence is presented in court

  • Standard procedures include

    • Recording the location of the evidence

    • Marking it for id (collector’s initials and date)

    • Properly completing evidence submission forms for lab analysis

    • Accounting for every person that handles or examines the evidence.


Obtain standard reference sample
Obtain Standard/Reference Sample

  • Examination often requires comparison with a known standardor referencesample

    • Hit and Run might require paint sample from car to compare to paint at scene

    • Bloodstained evidence must be compared to blood samples or buccal swaps from all people at the crime scene

  • Evidence may also be compared to substrate controls– materials adjacent to or close to areas where the evidence has been deposited

    • If a burned area is suspected to be covered in gasoline, it should be compared to a similar area not suspected

    • Bloodstains on garments should be compared to area without stains


Submit evidence to the laboratory
Submit Evidence to the Laboratory

  • Evidence is submitted by personal delivery or mail shipment depending on the location of the lab

  • Evidence submission forms should be completed which provides a brief history of the case, the evidence submitted, and the type of analysis that should be preformed

  • Analyst not strictly bound to specific test requested if new evidence is found or to search for trace evidence


Crime scene safety
Crime-Scene Safety

  • Because of the presence of biological substances with unknown pathogens, care should be taken to avoid contamination and infection

  • Guidelines set by the International Association for Identification Safety Committee include:

    • Wear protective gloves, shoe covers, liquid repellent coveralls

    • Mask/respirators, goggles, or face shields

    • Evidence possibly containing body fluids should be labeled as biohazard


Legal considerations at the crime scene
Legal Considerations at the Crime Scene

  • The removal of any evidence from a person or from the scene of crime must be done in conformity with the Fourth Amendment – the right against unreasonable searches

  • There are cases when police can justify a search without warrant


Legal considerations
Legal Considerations

  • Mincey v. Arizona

    • Undercover police officer, attempting to buy drugs, forced entry into the apartment and was killed

    • Without a search warrant, police searched the apartment for four days recovering bullets, drugs, and paraphernalia.

    • Evidence was submitted into trial but since it was illegally seized the court could not convict Mincey


Legal considerations1
Legal Considerations

  • Michigan v. Tyler

    • Loren Tyler and his business partner burned down leased property

    • Fire officials and police officers searched the premises after the smoke cleared, then 4 days,7 days, and 25 days later to collect evidence

    • Tyler and partner were convicted but it was overturned as searches were made without warrants (only initial evidence collected at first search was allowed)


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