Forensics Chapter 2 Flashcards

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Questions and Answers

Describe the differences between class and individual characteristics of evidence.

Class characteristics allow the item to be compared with a group, useful for eliminating possibilities. Individual characteristics allow comparison with a specific object or person, unique due to natural variation, damage, or wear.

What is Locard's Principle of Exchange?

Every contact leaves its trace.

What is mechanical fit?

Fracture matching where the fracture site can be lined up with the other side and individualized based on the fracture line.

What are latent prints?

Invisible prints created by the deposit of normal body secretions. Signup and view all the answers

What are patent prints?

Fingerprints caused by the deposit of contaminants like bloody or greasy finger marks. Signup and view all the answers

What are plastic prints?

Fingerprint impressions where a print has been deposited in a soft surface such as wax. Signup and view all the answers

Which method for DNA analysis is best for individualization in forensic work?

Short tandem repeat (STR) technology. Signup and view all the answers

What is Carl Sagan's famous adage about evidence?

The absence of evidence is not evidence of absence. Signup and view all the answers

What is the significance of mitochondrial DNA?

Mitochondrial DNA is inherited from the mother and can be used to compare questioned samples with maternal relatives. Signup and view all the answers

How can hairs be distinguished?

By species, and for human hair, by race and body location from which it originated. Signup and view all the answers

How are fibers classified?

Fibers are classified by their originating source: naturally occurring, manufactured, or synthetic. Signup and view all the answers

What is the loss rate of transferred hairs or fibers after contact?

90% of transferred hairs or fibers are lost in the first 8 hours. Signup and view all the answers

How is tape used to collect hair and fiber evidence?

A piece of tape is used to cover an area until tackiness reduces and then applied adhesive side down to plastic. Signup and view all the answers

What are the basic things glass is examined for?

Glass type, direction of force, and sequence of force. Signup and view all the answers

What is the 4R rule?

Ridge lines on radial fractures are at right angles to the rear. Signup and view all the answers

Which fragments can be used to evaluate glass fractures for direction of force?

Interior radial fracture fragments. Signup and view all the answers

What are radial fractures?

Fractures that radiate out from a central point. Signup and view all the answers

What are concentric fractures?

Fractures that encircle the central area at various distances. Signup and view all the answers

How is paint layering used in forensic analysis?

The sequence and layering of components can differentiate paint samples. Signup and view all the answers

What factors lead to environmental variations in soil samples?

Environmental contamination or unique environmental settings. Signup and view all the answers

What does firearms evidence consist of?

The weapon and any expended casings, bullets, or unexpended cartridges. Signup and view all the answers

What is stippling?

Embeddment of gunpowder particles in the skin during a close- or near-contact wound. Signup and view all the answers

What comprises typical ammunition anatomy?

A bullet, a casing, powder charge, and primer. Signup and view all the answers

What makes up shotgun cartridge anatomy?

A metal and plastic casing, shot, powder charge, and wadding. Signup and view all the answers

How does evaluating crime scene evidence differ between a pistol and a revolver?

Revolvers retain casings in the cylinder; pistols eject casings from the side once fired. Signup and view all the answers

What do rifling projections and depressions refer to?

Projections are lands and depressions are grooves that twist either right or left. Signup and view all the answers

What are bullet types based on firing mechanisms?

Single shot, semiautomatic, and automatic. Signup and view all the answers

What are fire arm class characteristics?

Caliber, shape of the firing chamber, location of the firing pin, and twist present in lands and grooves. Signup and view all the answers

How should bullets be marked for evidence?

They should not be marked directly and should be individually containerized. Signup and view all the answers

What do firearm individual characteristics arise from?

Microscopic variation from use, poor handling or cleaning, and marks from ejectors. Signup and view all the answers

Which is the better method for collecting tool mark evidence?

Collecting the entire tool mark itself. Signup and view all the answers

What are tire class characteristics?

Tread design, noise treatment, and tread-wear bars. Signup and view all the answers

What are tire individual characteristics?

Accidental marks or variations in wear. Signup and view all the answers

What is track width?

Measurement of the width across the front or rear axle. Signup and view all the answers

What is the most significant class characteristic in shoe mark examinations?

Tread design. Signup and view all the answers

What type of containers are used to collect fire scene evidence for accelerants?

Clean, unlined paint cans or glass jars. Signup and view all the answers

What is the difference between forged writing and traced writing?

Forged writing attempts to identify the writer of known notes; traced writing involves copying without fluid movement. Signup and view all the answers

What is the appropriate response for collecting a computer for analysis?

If off, photograph it, label connections, package cables securely; if running, check for destructive programs and document running programs. Signup and view all the answers

Study Notes

Class vs. Individual Characteristics

Class characteristics identify a group (e.g., vehicle type) and can eliminate possibilities (e.g., Jeep vs. Honda).
Individual characteristics are unique to a specific object or person (e.g., fingerprints, wear patterns).

Locard's Principle of Exchange

Every contact leaves a trace, emphasizing the importance of trace evidence.

Mechanical Fit

"Fracture matching" technique used to line up fracture sites for individualization based on fracture lines.

Latent Prints

Invisible fingerprints created by body secretions, not visible to the naked eye.

Patent Prints

Visible fingerprints caused by contaminants (e.g., grease or blood).

Plastic Prints

Fingerprint impressions made in soft materials like wax, leaving a three-dimensional print.

DNA Analysis Techniques

Short tandem repeat (STR) technology is the most effective for individualization in forensic cases, requiring minimal sample sizes.

Absence of Evidence

Carl Sagan stated, "The absence of evidence is not evidence of absence," highlighting the need for careful evidence interpretation.

Mitochondrial DNA (mDNA)

mDNA is inherited maternally and is useful in identifying relationships with decomposed bodies, especially with hair samples lacking roots.

Hair Analysis

Hairs can indicate species and, in human samples, general race and body location; usually classified, can sometimes be individualized.

Fiber Classification

Fibers are categorized based on their origin: natural, manufactured, or synthetic.

Trace Evidence Loss

Estimated that 90% of transferred hairs or fibers are lost within the first 8 hours after contact.

Tape Evidence Collection

Tape is applied to collect hair and fibers, ensuring separate pieces are used for different areas to avoid contamination.

Glass Examination

Glass analysis includes determining type, direction, and sequence of force; often involves class characteristics.

4R Rule for Glass Fractures

Ridge lines on radial fractures are perpendicular to the rear of the glass; used for identifying fracture direction.

Paint Sample Differentiation

Paint layering (primers, base coats, clear coats) helps distinguish samples; proper collection techniques are essential.

Soil Sample Comparison

Varied environmental factors contribute to soil sample differences; pollen evaluation is a useful comparative method.

Firearms Evidence

Analysis includes examining weapons and casings for association; distance determinations can be made through gunshot residue (GSR) patterns.

Stippling

Gunpowder particles embed in skin during close or near-contact wounds, indicating proximity to the shooting.

Ammunition Components

Cartridges consist of bullets, casings, powder charge, and primers.

Pistol vs. Revolver Evidence Collection

Revolvers retain casings internally; pistols eject spent casings, affecting evidence collection strategies.

Rifling Characteristics

Barrel rifling consists of lands (projections) and grooves (depressions) that determine bullet trajectory.

Types of Rifle Shots

Single-shot, semiautomatic, and automatic denote how ammunition is fed and fired.

Firearm Class Characteristics

Caliber, barrel shape, firing pin location, and rifling features serve as class characteristics for firearms.

Evidence Marking

Firearms and bullets should not be directly marked to preserve microscopic details; they must be properly containerized to prevent damage.

Tool Mark Evidence Collection

Collecting the actual tool mark is preferred over casting for accuracy and value retention.

Tire Characteristics

Class characteristics: tread design, noise treatment, tread-wear bars; individual characteristics arise from unique wear patterns.

Track Width Measurement

Defined by measuring the distance between the tracks on the front or rear axle, critical for crime scene analysis.

Shoe Mark Examination

Tread design serves as a major class characteristic for shoe marks, aiding in suspect identification through databases.

Collecting Fire Scene Evidence

Accelerants should be collected in unlined paint cans or glass jars to avoid contamination.

Distinction of Forged vs. Traced Writing

Forgeries mimic known writing to identify the author; tracing involves copying and lacks unique movement, preventing identification.

Collecting Computers for Forensic Analysis

If a computer is off: document connections, label cables, package securely. If it's on: identify destructive programs and document running processes before collecting.

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Description

Explore the key concepts of physical evidence in forensics through these flashcards. Understand the differences between class and individual characteristics, and how these traits help in criminal investigations. Perfect for students looking to grasp essential forensic principles.