Introduction to Forensic Science and Legal Standards

Definition: Forensic science is the application of the scientific method and techniques to the law and criminal justice.
Interdisciplinary Nature: It encompasses fields such as Chemistry, Physics, Biology, Anthropology, Psychology, and Mathematics.
Primary Function: To inform the court where it lacks expertise and provide a rational basis for interpreting scientific analysis.

Arthur Conan Doyle: Creator of Sherlock Holmes, based on real-life Prof. Joe Bell. He foretold many chemical analyses for forensic investigations.
Alphonse Bertillion: Developed Anthropometry, a system identifying individuals using body measurements (late $1800$ s).
Francis Galton: Pioneer in the study of Fingerprinting.
Calvin Goddard: Specialist in Ballistics.
Alexandre Lacassagne: Expert in Criminal Anthropology.
Edmond Locard: Established the first forensic laboratory ( $1877-1966$ ).

Locard’s Exchange Principle: The most basic concept in the field; whenever a criminal comes into contact with an object or person, a cross-transfer of evidence (dust, biological samples, fingerprints) occurs.
Principle of Individuality: Two objects may be indistinguishable, but no two objects are ever identical.

Context: Nineteen people were hanged and one pressed to death after Betty Parris ( $9$ ) and others exhibited strange behaviors (contortions, fever, hallucinations).
$1690$ s Medicine: Illness was often attributed to an imbalance of four humors: blood (hot), phlegm (cold), yellow bile (dry), and black bile (wet).
Scientific Hypothesis (Ergotism): Modern research suggests symptoms were caused by the ergot fungus (Claviceps purpurea) on rye. * Gangrenous Ergotism: Extremities turn black, mummify, and may break off. * Convulsive Ergotism: Fever, disorientation, hallucinations, and compulsive "strange dances" leading to exhaustion.

Frye Case ( $1923$ ): Established the "General Acceptance" standard; techniques must be accepted by a meaningful segment of the relevant scientific community.
Daubert Case ( $1993$ ): Replaced Frye in Federal courts; the judge acts as "gatekeeper" to determine reliability based on whether a theory has been tested, peer-reviewed, and has a known error rate.
General Electric v. Joiner ( $1995$ ): Ruled that the court may reject expert opinions where there is too great a gap between the existing data and the conclusion.
Kumho Tire Case ( $1999$ ): Extended the Daubert standard to include non-scientific expert testimony (technical/specialized knowledge).
Melendez-Diaz v. Massachusetts ( $2009$ ): Determined that lab analysts must testify in person rather than submitting certificates as evidence.

Functions of a Scientist: Examine evidence, perform analysis, render conclusions, and testify in court.
Lab Units: Biology, Firearms, Document Examination, Photography, Toxicology, Latent Fingerprints, etc.
Rationale: Labs have expanded due to the increasing volume of evidence, a rise in drug seizures, and legal decisions protecting defendant rights.

Physical Evidence: Includes Microscopy (hair/fiber matching), Ballistics (residue detection), Glass (refractive index), and Fingerprint identification.
Chemical/Biological Analysis: * Spectroscopy: Analyzes samples as a function of wavelength; includes FTIR and NMR. * SEM EDX: Scanning Electron Microscopy with Energy Dispersive X-ray for chemical composition. * Luminol: A chemiluminescent chemical used to detect blood at levels of $1\,\text{part per million}$ . * DNA Analysis: Used for individual identification and excluding suspects.
Forensic Specialties: Entomology (insects/time of death), Anthropology (skeletal identification), and Odontology (bite marks/dentistry).

Matter: Anything that has mass and occupies space. Physical properties (color, density) can be measured without changing the substance; chemical properties involve reactions.
Mixtures: Can be homogeneous (uniform) or heterogeneous. Separation methods include filtration, distillation, and chromatography.
Uncertainty: * Precision: How closely measurements agree with each other. * Accuracy: How closely measurements agree with the true value.
SI Base Units: Mass ( $kg$ ), Length ( $m$ ), Time ( $s$ ), Temperature ( $K$ ), and Amount ( $mol$ ).