Chapter 05
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This chapter discusses the importance of physical evidence in criminal investigations. It covers the evolution of forensic science, definitions of different types of evidence, guidelines for collecting, packaging, transporting, and storing evidence to maintain the chain of custody, and examples of frequently examined evidence types such as fingerprints, DNA, and tools. The chapter emphasizes properly handling evidence to avoid contamination and preserving evidence integrity throughout the entire investigation process.
Chapter 05
- 1. Chapter 5 Forensics/Physical Evidence Hess 5-1
- 2. 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 Hess 5-2
- 3. Definitions CATEGORIES • Testimonial • Documentary • Demonstrative • Physical Direct Indirect Hess 5-3
- 4. Investigative Equipment OVERVIEW • Selecting equipment • Equipment containers • Transporting equipment • Training in use Hess 5-4
- 5. Crime Scene Integrity and Contamination of Evidence VALUE OF EVIDENCE • Locard’s principle of exchange • Contamination • Integrity of evidence • Chain of evidence • Chain of custody Hess 5-5
- 6. Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal DISCOVERING OR RECOGNIZING EVIDENCE • Legally seized • Properly processed • Use common sense • Standard of comparison • Forensic light sources Hess 5-6
- 7. 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
- 8. 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
- 9. 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
- 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 Hess 5-10
- 11. Processing Evidence: Maintaining the Chain of Custody from Discovery to Disposal FINAL DISPOSITION OF EVIDENCE • Evidence must be legally disposed of • Returned to owner • Auctioned • Destroyed Hess 5-11
- 12. Frequently Examined Evidence FINGERPRINTS • Latent fingerprints • Visible fingerprints • Plastic fingerprints • Dusting latent fingerprints • Lifting prints Continued Hess 5-12
- 13. Frequently Examined Evidence (Continued) FINGERPRINTS • Chemical development • Other methods • Elimination prints • Inked prints • Digital fingerprinting Continued Hess 5-13
- 14. Frequently Examined Evidence (Continued) FINGERPRINTS • Fingerprint patterns, analysis and identification • Usefulness of fingerprints • Admissibility in court • Other types of prints Hess 5-14
- 15. Frequently Examined Evidence VOICEPRINTS • Graphic record made by a sound spectrograph • No two voiceprints are alike LANGUAGE ANALYSIS • Psycholinguistics • Excited utterances Hess 5-15
- 16. 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 Hess 5-16
- 17. 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 Hess 5-17
- 18. Frequently Examined Evidence SHOE AND TIRE PRINTS AND IMPRESSIONS • Can yield valuable investigative data BITE MARKS • Photograph if too shallow to cast • Forensic odontologist Hess 5-18
- 19. 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 Hess 5-19
- 20. Frequently Examined Evidence GLASS • High-velocity versus low-velocity impacts • Glass evidence reference database SOILS AND MINERALS • Forensic geologists • X-ray diffraction • Microscope Hess 5-20
- 21. 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 Hess 5-21
- 22. 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 Hess 5-22
- 23. 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 Hess 5-23
- 24. 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 Hess 5-24
- 25. 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 Hess 5-25
- 26. Frequently Examined Evidence OTHER TYPES OF EVIDENCE • Learn to read product DNA • Manufacturer codes • Discarded items • Lab can provide collecting and packaging instructions Hess 5-26
- 27. Evidence Handling and Infectious Disease 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
- 28. 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