Criminal Investigation Chapter 5: Forensics and Physical Evidence

Forensics and Physical Evidence

• Forensic science is the application of scientific processes to solve legal problems within the context of the criminal justice system.

Types of Evidence

• Best evidence: original evidence
• Physical evidence: anything real that helps establish facts of a case
• Direct evidence: establishes proof of a fact without other evidence
• Indirect evidence (circumstantial evidence): tends to incriminate a person
• Trace evidence: extremely small items (e.g., hair, fibers)
• Prima facie evidence: established by law
• Associative evidence: links a suspect with a crime (e.g., fingerprints, footprints)
• Corpus delicti evidence: establishes that a crime has been committed
• Probative evidence: vital to an investigation or prosecution
• Material evidence: forms a substantive part of a case
• Relevant evidence: applies to the matter in question
• Competent evidence: properly collected, identified, filed, and secured

Crime Scene Investigators

• CSI develops, processes, and packages physical evidence, attends and documents autopsies, and writes reports and testifies in court
• CSI effect: a phenomenon where TV shows create an unrealistic image of forensic science
• Tech effect: public awareness of modern technology influencing juror expectations

Investigative Equipment

• Equipment needed for each investigation varies
• Examples of equipment: cameras, chalk, containers, fingerprint kit, labels, magnifiers, measuring tape, notebooks, pens
• Selecting equipment: work with other organizations, identify what's needed, and select suitable equipment
• Equipment containers: store equipment carefully to maintain its condition
• Transporting equipment: use professional containers and equipment to create a consistent image

Crime Scene Integrity and Contamination of Evidence

• Value of evidence affected by what happens immediately following the crime
• Cordon off the crime scene to maintain integrity
• Document chain of evidence (chain of custody) to ensure admissibility in court
• Recall Locard's principle of exchange: collecting evidence can result in contamination

Processing Evidence: Maintaining the Chain of Custody

• Discovering or recognizing evidence: consider the type and nature of the crime, and examine the area carefully
• Marking, identifying, and collecting evidence: mark or identify each item, record date and time, and specify case number
• Packaging and preserving evidence: package each item separately to maintain integrity
• Transporting evidence: use legal ways to transport, specify signature upon receipt
• Protecting and storing evidence: store securely, free from pests, insects, and excessive heat or moisture
• Exhibiting evidence in court: ensure admissibility, identify evidence, describe where found, establish custody, and explain any changes

Frequently Examined Evidence

• Fingerprints: unique arrangement of friction ridges on fingertips

• Types of fingerprints:

  • Latent prints: not readily seen, developed through powders or chemicals
  • Visible fingerprints: made when fingers are dirty or stained
  • Plastic fingerprints: impressions left in soft substances

• Fingerprint analysis:

  • Elimination prints: identify whose prints belong at the scene
  • Inked prints: standard procedure for arrested adults
  • Digital fingerprinting: advances in computer technology
  • Fingerprint patterns, analysis, and identification: arched, looped, or whorled

• Voiceprints: graphic record of energy patterns emitted by speech

• Language analysis: captures spoken language, can reveal speaker's state-of-mind

• DNA profiling: uses genetic code to positively identify a person

• Human DNA profiling:

  • Uses material from chromosomes to identify individuals
  • Can be used to solve high-volume crimes
  • Identifying, collecting, and preserving DNA evidence
  • DNA testing: two types of DNA (nDNA and mtDNA)
  • Challenges with mixed profile samples
  • Y-STR analysis: uses Y chromosome as a male-specific identifier### DNA and Forensic Science

• The year-end backlog of offender DNA samples has increased steadily from 657,166 in 2007 to 952,393 in 2009.

• DNA can identify a criminal with near absolute certainty or exonerate innocent suspects.

• 325 people had been exonerated through DNA testing as of the time the text went to print.

Evidence Types

• Blood and other body fluids, including semen and urine, can provide valuable information.
• Semen and saliva may be detected with fluorescent lights (FLS), and blood trails or blood "spatter" can also be useful as evidence.
• Scent can establish probable cause for an arrest.
• Hairs and fibers can place an individual at the crime scene.
• Secondary ion mass spectrometry (SIMS) chemicals can distinguish trace hair samples using consumer chemicals as identifiers.
• Shoe and tire impressions can be specific to the shoe or tire.
• Bite marks can be found on the suspect or victim's body or on anything else placed in the mouth.
• Bite mark identification is based on the "supposed" individuality of teeth and is legally admissible in court.
• Teeth may also be an excellent source of genomic DNA.

Forensic Tools and Techniques

• Tools and tool marks can be traced if broken parts are left behind or by marks caused by the use of the tool.
• Firearms and ammunition can be analyzed through gunpowder tests, shot pattern tests, and functional tests of a weapon.
• Glass can be used for transfer of evidence and to show where a piece of glass came from at the crime scene.
• The Glass Evidence Reference Database contains more than 700 glass samples from manufacturers, distributors, and vehicle junkyards.
• Soils and minerals can place a suspect at a crime scene.
• Safe insulation can transfer to the suspect's clothing.
• Ropes, strings, and tapes can be compared, either by type or the cut ends.
• Drug identification kits can be used to make a preliminary analysis of a suspicious substance.
• Typing, handwriting, and printing can be compared.
• The Forensic Information System for Handwriting (FISH) is a database maintained by the U.S. Secret Service.
• Laundry and dry-cleaning marks can be used for comparisons and to find the business.
• Paint colors and samples can lead to the identification of an automobile.
• Digital evidence requires special handling and analysis.

Digital Evidence

• The digital revolution has generated a new class of evidence and requirements for handling it.
• The absence of geographic boundaries and the question of jurisdiction are challenges in electronic crimes.
• Cell phones can provide valuable evidence, including subscriber information, call-detail records, and GPS data.
• Only a person with training should analyze a cell phone.
• All cell phones leave a trail.
• Global positioning system chips built into cell phones allow authorities to track criminals as well as people in need of help.

Other Types of Evidence

• Weapons of mass destruction (WMDs) include nuclear weapons, radiological, biological or chemical agents, and explosives.
• Skeletal remains can be analyzed to determine whether they are animal or human.
• Dental comparisons and X-rays of old fractures are other important identifying features or individual characteristics.
• Wood comparisons are possible regarding the type of wood and origin.
• Prescription eyeglasses, broken buttons, glove prints, and other personal evidence found at a crime scene can also be examined and compared.
• Investigators should learn to read "product DNA," the printed code that appears on nearly every manufactured, mass-produced item.

Evidence Handling and Infectious Disease

• Consider all body secretions as potential health hazards.
• AIDS is not spread through casual contact such as touching an infected person or sharing equipment.
• Tuberculosis (TB) is of greater concern.
• MRSA is a staph infection that is resistant to most antibiotics and is very infectious, severe, and sometimes deadly.
• Use "universal precautions" when collecting blood evidence and other bodily fluids.
• Wash hands thoroughly with soap and water.
• Be alert for sharp objects, such as hypodermic needles and syringes, while processing the crime scene.