Chapter 5 - Forensics/Physical Evidence

Chapter 5

Forensics/Physical Evidence

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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

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Crime Scene Integrity and Contamination of Evidence

DISCOVERING OR RECOGNIZING EVIDENCE• Legally seized • Properly processed• Use common sense • Standard of comparison • Forensic light sources

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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

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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

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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

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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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FINGERPRINTS• Latent fingerprints• Visible fingerprints• Plastic fingerprints• Dusting latent

fingerprints• Lifting prints

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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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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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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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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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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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GLASS• High-velocity versus low-velocity impacts• Glass evidence reference

database

SOILS AND MINERALS• Forensic geologists • X-ray diffraction • Microscope

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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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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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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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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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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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OTHER TYPES OF EVIDENCE• Learn to read product DNA• Manufacturer codes• Discarded items• Lab can provide collecting and packaging instructions

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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

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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

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Chapter 5 - Forensics/Physical Evidence

Education