foresnic mid term friday

Forensic science

Application of science to questions of law.

CSI Effect

Media portrayals can shape public and juror expectations about forensic evidence.

Forensic science vs. criminology

Forensic science applies scientific methods to legal questions; criminology studies crime and criminal behavior.

Reproducibility

Repeated scientific analyses under appropriate conditions should yield comparable results.

Falsifiability

A scientific claim can be tested in a way that could potentially show it is wrong.

Peer review

Other qualified scientists evaluate methods, data, and conclusions.

Contextual bias

Case information not needed for testing may influence an examiner’s interpretation.

Sequential unmasking

Providing information to analysts in a controlled order to reduce bias.

Blind sample

A test sample whose identity or expected result is unknown to the analyst.

Positive control

A sample expected to produce a positive result.

Negative control

A sample expected not to contain the target substance or characteristic.

SOP

Standard Operating Procedure; written instructions for performing laboratory work.

Accreditation

Formal recognition that an organization meets specified standards.

Certification

Recognition that an individual meets specified professional requirements.

2009 NAS report

Highlighted the need for stronger scientific foundations, validation, standards, and consistency in forensic science.

Four federal forensic laboratories

FBI, DEA, ATF, and U.S. Postal Inspection Service.

Preponderance of evidence

Civil standard meaning more likely than not.

Beyond reasonable doubt

Higher burden of proof required for criminal conviction.

Trier of fact

Judge or jury responsible for deciding factual issues.

Ethics

Objectivity, honest reporting, proper procedures, and acknowledging scientific limitations.

Locard’s Exchange Principle

Contact creates opportunities for transfer of physical material.

Direct evidence

Evidence that directly establishes a fact if believed, without requiring an inference.

Circumstantial evidence

Evidence requiring an inference to connect it to a fact.

Class characteristics

Characteristics shared by a group of items or sources.

Individual characteristics

Characteristics that may strongly associate evidence with a particular source.

Inculpatory evidence

Evidence tending to support involvement or guilt.

Exculpatory evidence

Evidence tending to support innocence or exclude involvement.

Inclusion/association

Findings consistent with a proposed source; not always unique identification.

Exclusion

Meaningful differences rule out a proposed common source.

Inconclusive

Findings do not reliably support inclusion or exclusion.

Admissibility

Whether evidence may be considered in court.

Frye standard

Emphasizes general acceptance of a scientific method in the relevant field.

Daubert standard

Considers testability, peer review, error, standards, validation, and acceptance.

Rule 702

Federal rule governing expert testimony.

Judge as gatekeeper

Judge evaluates whether proposed expert evidence meets admissibility requirements.

Evidence does not prove

An association alone does not establish when transfer occurred or that a crime was committed.

Crime scene

Any location associated with an event under investigation.

Primary scene

Main location where the event of interest occurred.

Secondary scene

Additional location associated with the investigation.

Macro scene

Larger overall scene or area being investigated.

Micro scene

Smaller area or feature within a larger scene.

First responder priority

Protect life and safety before evidence preservation.

Entry log

Record of who entered a scene, when, and why.

Elimination sample

Known sample from someone legitimately present to help distinguish innocent traces.

Preliminary survey

Initial walk-through to identify hazards, evidence, boundaries, and processing needs.

Documentation methods

Notes, photos, video, sketches, measurements, mapping, and 3D scanning.

Photography sequence

Overall views, intermediate views, then close-ups.

Rough sketch

Sketch made at the scene showing layout, measurements, and evidence locations.

Final sketch

Cleaned-up representation based on original scene measurements.

LiDAR

Uses laser measurements to produce detailed 3D representations.

Search patterns

Systematic methods such as line, grid, spiral, zone, and wheel/ray.

Chain of custody

Documented record of evidence possession and transfers.

Why chain of custody matters

Helps establish evidence integrity and accountability.

Packaging separate items

Reduces cross-contamination.

Wet biological evidence

Should be handled to allow proper drying; avoid sealing wet material in airtight plastic.

Paper packaging

Commonly used for properly dried biological evidence because moisture can escape.

Control sample

Comparison material used to interpret an evidence sample.

Collection order

Locate, document, collect, package, secure, and record transfers.

Trace evidence

Small transferred materials such as fibers, glass, soil, paint, and residues.

Primary transfer

Direct movement of material from its original source to another surface.

Secondary transfer

Movement of material through an intermediate person or object.

Questioned sample (Q)

Sample recovered during investigation whose source is uncertain.

Known sample (K)

Reference sample from a documented source.

Stereo microscope

Provides a 3D-like view useful for preliminary examination and particle recovery.

Compound microscope

Uses transmitted light and higher magnification for suitable specimens.

Total magnification

Objective magnification multiplied by eyepiece magnification.

PLM

Polarized-light microscopy; useful for fibers, minerals, and optical properties.

Isotropic

Optical properties do not change with direction.

Anisotropic

Optical behavior changes with direction.

Birefringence

Difference in refractive indices associated with anisotropic materials.

Comparison microscope

Allows simultaneous side-by-side examination of two specimens.

MSP

Microspectrophotometry; objectively measures color characteristics.

Raman spectroscopy

Uses light scattering to obtain molecular information.

SEM/EDS

SEM images small features; EDS measures elemental composition.

Radial glass cracks

Cracks extending outward from an impact point.

Concentric glass cracks

Cracks forming around an impact point.

Refractive index

Optical property describing how light travels through a material.

Becke line

Bright halo used in refractive-index comparison.

Fiber comparisons

May examine color, morphology, cross-section, optical behavior, and chemistry.

Paint comparisons

May examine color, layer sequence, thickness, pigments, and composition.

Soil comparisons

May examine minerals, color, pH, particles, pollen, and optical properties.

Gunshot residue (GSR)

Inorganic particles associated with firearm discharge and ammunition primer.

GSR analysis

SEM/EDS evaluates particle shape and elemental composition.

Why “match” can be misleading

Shared class characteristics do not necessarily prove a unique common source.

Medicolegal death investigation

Investigation of questionable, sudden, suspicious, or unexplained deaths.

MDI

Medicolegal death investigator who examines circumstances, body, and scene information.

Coroner

Death-investigation official whose qualifications vary by jurisdiction.

Medical examiner

Physician-based death investigation official/system.

Forensic pathologist

Physician specializing in medical investigation of death and autopsy interpretation.

Cause of death

Disease or injury that begins the lethal chain of events.

Mechanism of death

Physiological or biochemical failure produced by the cause.

Manner of death

Natural, accident, suicide, homicide, or undetermined.

Homicide classification

Death caused by another person; not itself a legal finding of guilt.

PMI

Postmortem interval; estimated time elapsed since death.

Rigor mortis

Postmortem stiffening of muscles.

Rigor timing

Generally begins around 4 hours and may disappear around 24–36 hours; highly variable.

Livor mortis

Blood settling after death, causing discoloration.

Fixed lividity

Lividity that no longer blanches under pressure; often around 12 hours.

Algor mortis

Cooling of the body after death.

Algor rough estimate

About 1.5°C per hour for first 8 hours under specified conditions; not a universal rate.