Forensic Science Study Guide: Crime Scenes, Firearms & Trace Evidence

Vocabulary flashcards covering crime scene investigation procedures, ballistic and trace evidence analysis, and forensic case studies based on lecture material.

Due Process

A constitutional protection guaranteed by the 5th and 14th Amendments ensuring the government cannot deprive an individual of life, liberty, or property without following fair, established legal procedures.

Exclusionary Rule

A legal rule dictating that evidence collected via an illegal search in violation of the 4th Amendment may be ruled inadmissible in court, established in Mapp v. Ohio.

Chain of Custody

The documented, chronological record tracking everyone who collected, handled, transferred, or analyzed a piece of evidence to verify its integrity and prevent tampering or contamination.

Beyond a Reasonable Doubt

The highest standard of proof in the legal system, carried solely by the prosecution in criminal cases and rooted in the presumption of innocence.

Preponderance of the Evidence

The civil court standard of proof requiring an allegation to be demonstrated as more likely true than not (approximately $51\%$).

Locard's Exchange Principle

The foundational forensic principle stating that whenever two objects come into contact, a mutual exchange of physical material occurs ('every contact leaves a trace').

Primary Scene

The specific physical location where the criminal act originally took place.

Secondary Scene

A location associated with a crime other than where the primary event occurred, such as where a victim's body was moved or where a suspect fled.

Direct Evidence

Evidence that directly proves a fact on its own without requiring inferences, such as an eyewitness account, recorded video footage, or a confession.

Circumstantial Evidence

Evidence that requires an inference or logical deduction to connect it to a crime, including physical evidence like fingerprints and DNA.

Class Characteristics

Properties or traits of physical evidence associated with an entire group or category of items, such as bullet caliber or shoe model, that cannot identify an exclusive single source.

Individual Characteristics

Unique microscopic or physical traits of an item, such as fingerprint ridge patterns or microscopic barrel striations, that allow it to be attributed to an exclusive, singular source.

Integrated Ballistic Identification System (IBIS)

A digital imaging computer database system that captures microscopic tool marks on fired bullets and cartridge casings to search for and generate potential ballistic match leads.

National Integrated Ballistic Information Network (NIBIN)

The national firearms database network operated by the ATF that coordinates ballistic image comparisons generated by IBIS.

Comparison Microscope

A laboratory apparatus joining two microscopes with an optical bridge to permit side-by-side examination of ballistic striations or trace evidence within a single split field of view.

Caliber

The nominal bore diameter of a firearm barrel or projectile, measured across the interior lands and expressed in hundredths of an inch or millimeters.

Rifling

A series of spiral lands and grooves machined into the interior surface of a barrel that imparts gyroscopic spin to stabilize the bullet in flight.

Lands

The raised metal ridges situated between machined grooves inside a rifled gun barrel that imprint corresponding impressions onto fired projectiles.

3R Rule

A forensic glass analysis rule stating that Radial fractures form a Right angle on the Reverse side of the surface that received the force.

Striations

Microscopic scratch marks carved onto projectiles and cartridge cases by imperfections, wear patterns, and machining marks inside a firearm.

Smokeless Powder

A modern propellant composed of nitrocellulose (single-base) or nitrocellulose combined with nitroglycerin (double-base) formulated to produce minimal smoke.

Gunshot Residue (GSR)

Microscopic combustion particles expelled during the discharge of a firearm, definitively identified by the combined presence of lead (Pb), barium (Ba), and antimony (Sb).

SEM-EDS

Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, serving as the standard confirmatory diagnostic instrument for gunshot residue detection.

Trace Evidence

Minute quantities of physical material transferred between persons, objects, or crime scenes in accordance with Locard's Exchange Principle.

Paper Bindle

A folded paper packet used to secure and preserve small, delicate items of trace evidence from loss or contamination.

Premeditation

A conscious, fully formed intent to kill formulated with sufficient time prior to the act to permit conscious reflection.

Investigative Genetic Genealogy (IGG)

An investigative technique that evaluates single-nucleotide polymorphism (SNP) DNA profiles against public databases to identify candidates through constructed familial trees.

Forensic Odontology

The application of dental science to legal investigations, used decisively in the Helle Crafts case to identify victim remains via dental X-rays and tooth caps.

McHoul Test

The Massachusetts legal standard establishing lack of criminal responsibility if a defendant lacked substantial capacity to appreciate the wrongfulness of their conduct or conform to the law due to a mental disease or defect.