hosa forensic science

Definition: The application of scientific principles and methods to criminal and civil laws.
Key Principles:
- Locard's Exchange Principle: "Every contact leaves a trace." When two objects come into contact, there is a transfer of material.
- Identification: Determining the physical or chemical identity of a substance.
- Comparison: Ascertaining whether two or more objects have a common origin.

First Responder Duties: Secure the scene, render aid, detain witnesses, protect the evidence.
Documentation: Critical for maintaining the integrity of the scene and evidence.
- Photography: Comprehensive visual record (overall, midrange, close-up with scale).
- Sketching: Rough sketch and finished sketch (measurements, evidence placement).
- Notes: Detailed written record of observations, actions, and evidence.
Evidence Collection and Preservation:
- Chain of Custody: A documented unbroken transfer of evidence from crime scene to court.
- Packaging: Proper packaging to prevent contamination and degradation (e.g., paper bags for biological evidence, airtight containers for arson).
- Search Patterns: Spiral, grid, strip/line, quadrant/zone.

Types: Arches, Loops ( $60\%$ of population), Whorls ( $35\%$ of population).
Detection & Collection: Powders, chemical methods (ninhydrin, super glue fuming), alternate light sources.
AFIS (Automated Fingerprint Identification System): Database for comparing prints.

Structure: Double helix, composed of nucleotides (adenine, guanine, cytosine, thymine).
Collection: Biological fluids (blood, semen, saliva), hair with follicle, skin cells.
Analysis:
- PCR (Polymerase Chain Reaction): Amplifies tiny amounts of DNA.
- STR (Short Tandem Repeats): Specific regions of DNA used for comparison.
- Electrophoresis: Separates DNA fragments by size.
- CODIS (Combined DNA Index System): National DNA database.

Hair: Morphology (medulla, cortex, cuticle), human vs. animal, treated vs. natural. Not individual evidence without follicle/DNA.
Fibers: Natural (cotton, wool), synthetic (nylon, polyester). Color, diameter, cross-section, chemical composition for comparison.
Glass: Density, refractive index ( $n = \frac{c}{v}$ ), fracture patterns (radial, concentric).
Soil: Color, texture, mineral content, pH. Can link a suspect to a scene.

Firearms: Handguns, rifles, shotguns.
Ammunition: Cartridge components (case, primer, propellant, bullet).
Analysis: Bullet striations, firing pin impressions, breech block marks on cartridge cases.
NIBIN (National Integrated Ballistic Information Network): Database for firearm evidence.

Forensic Pathology: Medical examination of deaths (autopsies) to determine cause, manner (homicide, suicide, accidental, natural, undetermined), and mechanism of death.
Forensic Entomology: Study of insects associated with a cadaver to determine time of death (Post Mortem Interval - PMI).
Forensic Anthropology: Analysis of skeletal remains for identification (age, sex, ancestry, stature) and trauma.
Forensic Toxicology: Detection and identification of drugs and poisons in body fluids and tissues.
Forensic Odontology: Examination of dental evidence for identification (dental records) and bite mark analysis.
Forensic Document Examination: Analysis of handwriting, typewriting, alterations, and forged documents.
Digital Forensics: Recovery and investigation of material found in digital devices.

Admissibility of Evidence:
- Frye Standard (1923): Scientific evidence must be "generally accepted" by the scientific community.
- Daubert v. Merrell Dow Pharmaceuticals (1993): Replaced Frye for federal courts, emphasizing judge as "gatekeeper" for scientific reliability.
Expert Witness: An individual with specialized knowledge who provides testimony based on their expertise.