crj310 chap5
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Chapter 5
Forensics/Physical Evidence
Hess 5-1
Introduction• Evolution of law enforcement has benefited greatly
from forensic science• Forensic science dates back to 1910 and the “exchange
principle” set forth by French criminologist Edmond Locard
• Primary purpose of an investigation is to locate, identify and preserve evidence
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CATEGORIES• Testimonial• Documentary• Demonstrative• Physical
Direct Indirect
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Definitions
OVERVIEW• Selecting equipment• Equipment containers• Transporting equipment• Training in use
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Investigative Equipment
VALUE OF EVIDENCE• Locard’s principle of exchange• Contamination• Integrity of evidence • Chain of evidence• Chain of custody
Hess 5-5
Crime Scene Integrity and Contamination of Evidence
DISCOVERING OR RECOGNIZING EVIDENCE• Legally seized • Properly processed• Use common sense • Standard of comparison • Forensic light sources
Hess 5-6
Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
MARKING, IDENTIFYING AND COLLECTING EVIDENCE• Mark, log, photograph
and collect all objects• Requires judgment and care• Avoid cross-contamination• Make marks recognizable
and small as possible
Hess 5-7
Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
PACKAGING AND PRESERVING EVIDENCE• Package each item separately• Specific requirements for that type of evidence• Both plastic and paper forms of packaging available• Preserve evidence on immovable items at the scene• Transmittal letter
Hess 5-8
Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
TRANSPORTING EVIDENCE• Can deliver personally• Use fastest method available
PROTECTING, STORING AND MANAGING EVIDENCE
• All evidence received is recorded in a register• Some evidence requires more care than others• Automated storage
Hess 5-9
Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
Hess 5-10
Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
EXHIBITING EVIDENCE IN COURT• Identify the evidence as that found at the scene• Describe exactly where it was found• Establish its custody • Voluntarily explain any changes that have occurred
FINAL DISPOSITION OF EVIDENCE• Evidence must be legally disposed of• Returned to owner• Auctioned • Destroyed
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Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal
FINGERPRINTS• Latent fingerprints• Visible fingerprints• Plastic fingerprints• Dusting latent
fingerprints• Lifting prints
ContinuedHess 5-12
Frequently Examined Evidence
FINGERPRINTS• Chemical development• Other methods• Elimination prints• Inked prints• Digital fingerprinting
Continued
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Frequently Examined Evidence (Continued)
FINGERPRINTS• Fingerprint patterns, analysis and identification• Usefulness of fingerprints• Admissibility in court• Other types of prints
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Frequently Examined Evidence (Continued)
VOICEPRINTS• Graphic record made by a sound spectrograph• No two voiceprints are alike
LANGUAGE ANALYSIS• Psycholinguistics• Excited utterances
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Frequently Examined Evidence
HUMAN DNA PROFILING• Identifying, collecting and preserving DNA evidence• Moral and ethical issues
BLOOD AND OTHER BODY FLUIDS• Luminol• Bloodstains• Spatter patterns
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Frequently Examined Evidence
SCENT • Every person has a unique scent• Scent pads can be presented to a tracking dog
HAIRS AND FIBERS • Examining hair• Examining fibers
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Frequently Examined Evidence
SHOE AND TIRE PRINTS AND IMPRESSIONS • Can yield valuable investigative
data
BITE MARKS• Photograph if too shallow
to cast • Forensic odontologist
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Frequently Examined Evidence
TOOLS AND TOOL MARKS• Common tools are often used in crimes• Tool mark is an impression left by a tool on a surface
FIREARMS AND AMMUNITION• Many violent crimes are committed with a firearm• Gunshot residue (GSR)• Shooter ID kits
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Frequently Examined Evidence
GLASS• High-velocity versus low-velocity impacts• Glass evidence reference
database
SOILS AND MINERALS• Forensic geologists • X-ray diffraction • Microscope
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Frequently Examined Evidence
SAFE INSULATION• Few people normally come into contact with safe insulation
ROPES, STRINGS AND TAPES• Laboratories have various comparison standards • Fingerprints can occur on either side of a tape
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Frequently Examined Evidence
DRUGS• Put drugs in a bottle and attach label• Solid drugs in a pillbox
WEAPONS OF MASS DESTRUCTION• Designed to produce substantial damage• Acronyms
CBRNE
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Frequently Examined Evidence
DOCUMENTS• Do not touch documents with bare hands• Identify cellophane/manila envelopes on the outside
DIGITAL EVIDENCE • Pervasive nature of cell phones• Digital forensic courses
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Frequently Examined Evidence
LAUNDRY AND DRY-CLEANING MARKS• Many launderers and dry cleaners use specific marking
systems• Submit the entire garment to a laboratory
PAINT• Paints are complex and are individual • Use small boxes for submitting paint samples to the crime
lab
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Frequently Examined Evidence
SKELETAL REMAINS• Determine whether remains are animal or human• Forensic anthropology
WOOD• If found wet, keep it wet• If found dry, keep it dry
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Frequently Examined Evidence
OTHER TYPES OF EVIDENCE• Learn to read product DNA• Manufacturer codes• Discarded items• Lab can provide collecting and packaging instructions
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Frequently Examined Evidence
PRECAUTIONS• Likely to encounter infectious body fluids• Universal precautions• Consider all body secretions as potential health
hazards• Constantly be alert for sharp objects• After processing, decontaminate the crime scene
Hess 5-27
Evidence Handling and Infectious Disease
Summary• Criminal investigations rely heavily on various types of
evidence• The more individual the evidence, the greater its value• Mark or identify each item of evidence • Package evidence properly • Document custody of the evidence at every stage• After a case is closed, evidence is returned to the
owner, auctioned or destroyed
Hess 5-28
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