Criminal Investigations: Forensics and Physical Evidence

Forensic Science and Physical Evidence

• Forensic science is the application of scientific processes to solve legal problems, notably within the context of the criminal justice system.
• Crime scenes always leave behind incriminating evidence, known as proxy data.

Types of Evidence

• Best evidence: original evidence
• Physical evidence: anything with substance that helps establish the 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, such as hair or fibers
• Prima facie evidence: evidence established by law
• Associative evidence: links a suspect with a crime (e.g., fingerprints, footprints, bloodstains, hairs, and fibers)
• Corpus delicti evidence: establishes that a crime has been committed
• Probative evidence: vital to the investigation or prosecution of a case
• Material evidence: forms a substantive part of the case
• Relevant evidence: applies to the matter in question
• Competent evidence: properly collected, identified, filed, and secured

Crime Scene Investigators (CSIs)

• CSIs develop, process, and package physical evidence, transport it to the lab for forensic evaluation, attend and document autopsies, and write reports and testify in court.
• The CSI effect: a phenomenon that has created a glamorized, impractical image of the field.
• The tech effect: public awareness of modern technology influencing juror expectations.

Investigative Equipment

• Equipment needed for each type of investigation varies.
• Specialized equipment includes cameras, chalk, containers, fingerprint kits, labels, magnifiers, measuring tape, notebooks, pens, and laptops.
• Selecting equipment:
  • Work with other organizations to identify needs.
  • Select equipment based on organizational needs.
• Equipment containers:
  • Use professional containers and equipment to create a consistent image.
  • Care for equipment to ensure it works when needed.
• Transporting equipment:
  • Use police cars, specially equipped vehicles, or mobile crime labs.
• Training in equipment use:
  • Lack of training is a common cause of equipment failure.

Crime Scene Integrity and Contamination of Evidence

• The value of evidence is directly affected by what happens to it immediately following the crime.
• Cordon off the crime scene to maintain integrity.
• Document everything: what has happened to the evidence from discovery to the present.
• Recognize potential evidence:
  • Examined objects unrelated or foreign to the scene.
  • Unusual items in location or number, or damaged or broken objects that fit a pattern that suggests a crime.

Processing Evidence: Maintaining the Chain of Custody

• Discovering or recognizing evidence:
  • Consider the type and nature of the crime.
  • Examine objects in the area of the crime scene.
  • Recall the Brady rule: gather all evidence that helps establish guilt or innocence.
• Marking, identifying, and collecting evidence:
  • Mark or identify each item of evidence in a way that can be recognized later.
  • Record the date and time of collection, where the evidence was found, and by whom.
  • Package each item separately in a durable container.
• Transporting evidence:
  • Use registered mail, insured parcel post, air express, or Federal Express.
  • Specify that the person receiving the evidence is to sign for it.
• Protecting and storing evidence:
  • Store evidence in a secure, pest-free, and climate-controlled environment.
  • Manage property effectively to accommodate the increasing amount of evidence.

Frequently Examined Evidence

• Biometrics: the statistical study of biological data.

• Fingerprinting:

  • 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.
  • Dusting latent fingerprints: be careful not to over-process.
  • Lifting prints: use black lifters for light powders and light lifters for dark powders.

• Voiceprints:

  • Graphic record of the energy patterns emitted by speech.
  • Like fingerprints, no two voiceprints are alike.

• DNA Profiling:

  • Deoxyribonucleic acid (DNA) is the building block of chromosomes.
  • Genetic code can be used to create a genetic fingerprint to positively identify a person.### DNA and Forensic Analysis

• The national backlog of offender DNA samples increased from 657,166 in 2007 to 952,393 in 2009.

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

• As of the time the text was written, 325 people had been exonerated through DNA testing.

Biological Evidence

• Blood and other body fluids, including semen and urine, can provide valuable information.
• Semen and saliva can be detected with fluorescent lights.
• Blood trails or blood "spatter" can be useful as evidence.
• Every person has a unique scent that cannot be masked or eliminated.
• Hairs and fibers can place an individual at the crime scene, especially in violent crimes.
• Secondary ion mass spectrometry (SIMS) can distinguish trace hair samples using consumer chemicals as identifiers.

Shoe and Tire Impressions

• Tracks or marks left by shoes or tires can be specific to the shoe or tire.

Bite Marks

• 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 individuality of teeth and is legally admissible in court.
• Teeth may also be an excellent source of genomic DNA.

Tools and Tool Marks

• Tools can be traced if broken parts are left behind or by marks caused by the use of the tool.

Firearms and Ammunition

• Gunpowder tests, shot pattern tests, and functional tests of a weapon can be made and compared.
• Firearm evidence can include bullets, shell casings, slugs, shot pellets, and gunshot residue.

Glass Evidence

• 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

• Soil and mineral analysis can place a suspect at a crime scene.

Other Types of Evidence

• Safes contain insulation that 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.
• Documents, such as typing, handwriting, and printing, can be compared.
• 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, such as cell phones, pagers, and computers, can generate a new class of evidence.
• Each cell phone provider stores and maintains subscriber records, including subscriber information and call-detail records.
• Global positioning system (GPS) chips built into cell phones allow authorities to track criminals.

Weapons of Mass Destruction (WMDs)

• Testing matrixes include aerosols, liquids, solids, surfaces, and dermal samples.
• At any WMD crime scene, the public's safety takes precedence over evidence collection.

Skeletal Remains

• Laboratories can determine whether skeletal remains are animal or human.
• Dental comparisons and X-rays of old fractures are other important identifying features.

Wood and Other Types of Evidence

• 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.

Evidence Handling and Infectious Disease

• All body secretions should be considered as potential health hazards.
• AIDS is not spread through casual contact.
• 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.
• Universal precautions should be used when collecting blood evidence and other bodily fluids.
• Hands should be washed thoroughly with soap and water.