FBI Forensic Science & Analysis 2 — Questions and Answers
Question 1: When collecting gunshot residue (GSR) from a suspect's hands, which collection method is considered the gold standard for subsequent SEM-EDX analysis?
- Adhesive stub (carbon tape) swabs (Correct answer)
- Cotton swab moistened with distilled water
- Nitric acid wipe
- Dry filter paper collection
Correct 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.
Question 2: 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?
- Smith & Wesson
- Colt (Correct answer)
- Glock
- Ruger
Correct 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.
Question 3: In bloodstain pattern analysis, a 'satellite' stain is best defined as:
- A stain caused by secondary impact droplets projected from a parent stain (Correct answer)
- A circular stain indicating a drop fell from a height greater than 6 feet
- A transfer pattern left by a bloody shoe
- A void pattern indicating an object blocked the blood source
Correct 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.
Question 4: Which chemical reagent is most commonly used to visualize latent fingerprints on porous surfaces such as paper by reacting with amino acids?
- Cyanoacrylate fuming
- Ninhydrin (Correct answer)
- Luminol
- Sudan Black
Correct 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.
Question 5: 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?
- Random Match Probability (RMP)
- Likelihood Ratio (LR) (Correct answer)
- Combined Probability of Inclusion (CPI)
- Hardy-Weinberg Equilibrium coefficient
Correct 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.
Question 6: 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?
- Extractor groove
- Primer face (Correct answer)
- Case mouth
- Cannelure
Correct 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.
Question 7: 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?
- Luminol destroys all subsequent DNA evidence
- Luminol can produce false positives with certain household cleaners and plant peroxidases (Correct answer)
- Luminol only reacts with arterial blood, not venous blood
- Luminol testing is inadmissible in federal court
Correct 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.
FBI Forensic Science & Analysis 2
When collecting gunshot residue (GSR) from a suspect's hands, which collection method is considered the gold standard for subsequent SEM-EDX analysis?