Introduction to Forensic Science

Definition and scope of forensic science?

The application of scientific methods and techniques to matters of law. Involving collecting, preserving, analyzing, and interpreting evidence for criminal and civil investigations.

Sections of the American Academy of Forensic Sciences?

Criminalistics, Forensic Biology, Forensic Chemistry, Forensic Medicine, Digital and Multimedia Sciences, Forensic Psychology, Forensic Sociology, Questioned documents

Locard’s Exchange Principle

"every contact leaves a trace," meaning when two people or object come into contact, material may be transferred between them.

Organization and growth of crime labs in the United States

U.S crime labs operate at the federal, state, county, and local levels. They expanded due to advances in forensic technology, DNA testing, and greater reliance on scientific evidence.

Services/units of crime laboratories and functions

Biology/DNA, toxicology, firearms, latent fingerprints, trace evidence, digital evidence, and questioned documents.

Functions/role of forensic scientist

Examines and analyzes physical evidence, prepares reports, maintains records, may testify as an expert witness in court.

Steps of securing and surveying the crime scene

Ensure safety and aid injured people → secure and establish boundaries → restrict/document access → prevent contamination → conduct an initial walkthrough → identify potential evidence → develop a plan for documenting, searching, and processing the scene.

Search patterns

Line search, grid search, zone search, and spiral search.

Different methods of recording the crime scene

Photographs, videos sketches, and notes.

Hand written notes

Create an immediate written record but can be slower.

Audio-recorded notes.

Allow quick, detailed observations but must be properly preserved and may need to be transcribed.

Film photography

A method of capturing images on light-sensitive film, used in crime scene documentation to provide visual evidence that can be analyzed later. Commonly used before digital photography became standard.

Digital Photography

A modern method of capturing images using electronic sensors, allowing immediate review and manipulation of images, widely used in crime scene documentation for its speed and efficiency.

DSLR cameras

Digital Single-Lens Reflex cameras that capture high-quality images using a mirror mechanism, often utilized in forensic photography for their versatility and excellent performance in various lighting conditions.

Wide-angle lens

A type of lens with a focal length shorter than standard, providing a wider field of view, commonly used in forensic photography to capture large areas/rooms.

Standard lens

A lens with a focal length typically around 50mm, offering a natural perspective similar to the human eye, often used in forensic photography for its balanced field of view.

Telephoto

lens is designed to magnify distant subjects, providing a narrow field of view, commonly used in forensic photography to capture detailed images from afar without being intrusive.

Macro lens

Captures close-up details and small evidence.

Video Documentation

Records the scene continuously and can demonstrate the overall layout and relationship between areas.

Crime scene sketching

A hand-drawn or computer-generated documentation that records the exact layout of a crime scene and the spatial relationships between evidence and fixed objects.

Chain of custody

The documented history of who collected, handled, transferred, examined, and stored evidence from collection through its use in court.

Standard/reference samples

A sample from a known source used for comparison with questioned evidence, such as a known DNA sample or known paint sample.

Substrate samples

A sample of the surface or material surrounding evidence, collected to determine whether the substrate itself could affect testing or results.

Personal protective equipment/gear

Gloves, masks, eye protection, protective clothing, and shoe coverings are used to protect personnel and prevent contamination of evidence.

Fourth Amendment

Protects against unreasonable searches and seizures.

Fundamentals of scene reconstruction

Using physical evidence and scientific reasoning to determine what likely occurred and the sequence/relationships of events at a scene.

Objectivity

The evaluation of evidence without allowing personal beliefs, expectations, or bias to determine the conclusion. Conclusions should be based on evidence

Inductive Reasoning

Moves from specific observations to a broader explanation or generalization. Evidence → possible/general conclusion.

Deductive reasoning

Uses a hypothesis to predict or evaluate a specific situation. General idea → specific expected result.

Falsifiability

A scientific hypothesis must be capable of being tested and potentially shown to be false by evidence.

Bifurcation

Treating an investigation as only two competing possibilities, which can cause investigators to overlook other reasonable explanations.

Generalization

Drawing a broader conclusion from observations or evidence.

False linkage

Incorrectly connecting people, objects, evidence, or events that are not actually associated.

Types of evidence used in scene reconstruction

Bloodstain patterns, fingerprints, DNA, trace evidence, firearms evidence, injuries, impressions, documents, digital evidence, and the locations/relationships of objects.

Theory formation

Developing a testable explanation of events based on available evidence, then evaluating that explanation against additional evidence.

Timeline charts

Visual representations that arrange events in chronological order to help reconstruct when and in what sequence events occurred.

Identification

Determining the physical or chemical identity of a substance or item using accepted analytical methods.

Comparison

Examining a questioned sample and a known/reference sample to evaluate their similarities and differences.

Individual characteristics

Unique, microscopic, or random features on an object or person that can link evidence to a single, specific source with a high degree of certainty,

Class characteristics

Link evidence to a shared category or group, rather than one unique source.

Product rule

A statistical method used to estimate the probability of independent characteristics occurring together by multiplying their individual probabilities.

Value of evidence

Depends on factors such as its relevance, reliability, quality, rarity, condition, context, and ability to associate or exclude people/objects.

Rapid DNA

Automated technology designed to produce a DNA profile much faster and with less manual processing.

Forensic palynology

The forensic examination of pollen and spores

Pollen spores

Microscopic biological materials that can transfer to clothing, objects, vehicles, or people.

CODIS

Combined DNA Index System — a system used by U.S. law-enforcement laboratories to store and compare qualifying DNA profiles and help identify potential matches.

AFIS / NGI

Automated Fingerprint Identification System / Next Generation Identification — systems used to search and compare fingerprint and other biometric records.

NIBIN

National Integrated Ballistic Information Network — used to compare digital images of markings on fired cartridge cases and help identify possible links between firearm-related cases.

PDQ

Paint Data Query — a database containing automotive paint information that can assist with identifying or comparing vehicle paint evidence.

SICAR

Shoe print Image Capture and Retrieval — a system/database used to help compare and identify footwear impression evidence.

Forensic entomologist

Studies insects associated with remains to help estimate the time since death and provide information about the circumstances of death.

Forensic Anthropologist

Examines human skeletal remains to help identify individuals and determine characteristics such as age at death, biological sex, and evidence of skeletal trauma.

Forensic Odontologist

Uses dental records, teeth, and other dental evidence to assist with human identification and investigations.

Line/Strip Search

One or two investigators start at the boundary at one end of the scene and walk straight across to the other side. They then move farther along the border and walk straight back to the other side, repeating the process.

Grid Search Pattern

Two searchers originate at adjacent ends of the area and search the scene in perpendicular lines, overlapping to ensure thorough coverage of the area.

Spiral Search Pattern

Usually employs one person who moves in an inward spiral from the outer edge to the center of the scene or in an outward spiral from center of the scene to the outside.

Wheel/Ray Search pattern

Employs several people who search in straight lines toward the center of the scene.

Quadrant / Zone Search

Divides the scene into zones or quadrants; members are assigned to each section, best suited for larger areas.