Forensic Science

1. Introduction to Forensic Science

  • Definition & Scope: Forensic science is the application of science to investigate crimes and examine evidence. It is considered an applied science because it takes scientific principles and methods from pure sciences to solve real-world legal problems.

  • Scientific Disciplines Applied:

    • Biology

    • Chemistry

    • Physics

    • Geology

2. Pioneers and Key Contributions

  • Mathieu Orfila: Helped establish forensic toxicology, especially the study of poisons and drugs.

  • Alphonse Bertillon: Developed anthropometry, a system using body measurements to identify individuals.

  • Francis Galton: Helped establish fingerprints as a method of identifying individuals.

  • Leone Lattes: Developed methods for bloodstain typing from dried bloodstains.

  • Calvin Goddard: Used a comparison microscope to compare bullets and firearm evidence.

  • Albert S. Osborn: Made major contributions to questioned-document examination and handwriting analysis.

  • Hans Gross: Wrote the first comprehensive treatise advocating the application of scientific disciplines to criminal investigation, helping establish forensic investigation as a systematic field.

3. Core Principles & Trace Evidence

  • Locard's Exchange Principle: States that when two objects come into contact, material is transferred between them (e.g., hair, fibers, or particles).

  • Trace Evidence Considerations:

    • Similar fiber evidence does not conclusively prove a suspect was at a crime scene because other sources may produce similar fibers.

  • Sources of Error:

    • Contamination: Can alter evidence, produce inaccurate results, and lead to incorrect conclusions.

    • Measurement or Observation Errors: Inaccuracies in data collection or interpretation.

4. Crime Laboratory Units & Forensic Specialties

  • Five Standard Crime-Lab Units:

    • Biology: Examines biological fluids, DNA, and organic matter.

    • Chemistry / Trace Evidence: Examines materials such as hair, fibers, and unknown substances.

    • Firearms: Examines bullets, cartridge cases, and ballistic evidence.

    • Questioned Documents: Examines handwriting, anonymous notes, and document integrity.

    • Fingerprints: Processes and analyzes latent fingerprints.

  • Optional / Specialized Units:

    • Forensic Pathology: Examination of death and cause of death.

    • Forensic Anthropology: Examination of bones and human skeletal remains.

    • Forensic Entomology: Study of insects in relation to criminal investigations and time of death.

    • Forensic Odontology: Examination of teeth and bite mark evidence.

    • Forensic Psychiatry / Engineering / Photography / Toxicology: Specialty areas for psychological profiling, structural failure analysis, scene documentation, and drug/poison detection.

5. Postmortem Changes

  • Rigor Mortis: Stiffening of body muscles after death.

  • Livor Mortis: Settling of blood in lower regions of the body after death, causing skin discoloration.

  • Algor Mortis: Cooling of the body temperature after death.

6. Legal Standards for Scientific Evidence

  • Frye Standard: Mandates that scientific evidence or techniques must be generally accepted by the relevant scientific community to be admissible in court.

  • Daubert v. Merrell Dow Pharmaceuticals: Established that judges act as "gatekeepers" deciding whether scientific evidence is reliable and admissible.

  • Daubert Criteria:

    • Testing of the scientific technique or theory.

    • Peer review and publication.

    • Known or potential error rate.

7. Scientific Method & Investigation

  • Functions of a Forensic Scientist: To examine physical evidence and interpret or explain the findings.

  • Scientifically Testable Questions: Must be focused, measurable, and testable.

  • Data Types:

    • Observation: Directly seen, measured, or detected fact.

    • Inference: Conclusion drawn from observations or evidence.

  • Variables:

    • Independent Variable: The factor changed or manipulated by the investigator.

    • Dependent Variable: The factor measured to determine the outcome.

    • Controlled Variables: Factors kept constant to ensure a fair test.

  • Objective Reporting: Scientists must report all findings, including those that do not support their hypothesis, to maintain objective, evidence-based conclusions.