Forensic Science & Analysis Flashcards

When collecting gunshot residue (GSR) from a suspect's hands, which collection method is considered the gold standard for subsequent SEM-EDX analysis?

Answer: Adhesive stub (carbon tape) swabs

Adhesive carbon tape stubs preserve GSR particle morphology and elemental composition for scanning electron microscopy with energy-dispersive X-ray analysis.

A fired bullet recovered at a scene shows six lands and grooves with a right-hand twist. This rifling characteristic is MOST consistent with firearms manufactured by which company?

Answer: Colt

Colt firearms are known for their six lands and grooves with a left-hand twist, while Smith & Wesson typically uses five lands and grooves with a right-hand twist — making this bullet more consistent with S&W.

In bloodstain pattern analysis, a 'satellite' stain is best defined as:

Answer: A stain caused by secondary impact droplets projected from a parent stain

Satellite stains are small secondary droplets that break away from a parent blood drop upon impact, scattering around the main stain.

Which chemical reagent is most commonly used to visualize latent fingerprints on porous surfaces such as paper by reacting with amino acids?

Answer: Ninhydrin

Ninhydrin reacts with amino acids in sweat residue on porous surfaces to produce a purple compound called Ruhemann's purple, revealing latent prints.

During a homicide investigation, touch DNA is swabbed from the grip of a firearm. The sample yields a mixed profile with two contributors. Which statistical measure is used to report the evidential weight of this mixed profile?

Answer: Likelihood Ratio (LR)

The Likelihood Ratio compares the probability of the evidence given the suspect is a contributor versus a random person, making it the preferred metric for mixed DNA profiles.

An agent finds cartridge cases at a shooting scene. Which area of the cartridge case is MOST useful for comparing firing pin impressions to a suspected firearm?

Answer: Primer face

The primer face receives the direct impression of the firing pin, making it the primary surface for microscopic comparison to the suspected firearm's firing pin.

Luminol testing at a crime scene produces a positive chemiluminescent reaction in an area that has been cleaned with bleach. What is the most important limitation agents must consider?

Answer: Luminol can produce false positives with certain household cleaners and plant peroxidases

Luminol produces false-positive reactions with bleach, copper, and plant-based peroxidases, so positive results require confirmation with additional presumptive and confirmatory tests.