FBI Forensic Science & Analysis 2

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?

Accepted Answer

Adhesive stub (carbon tape) swabs

Answer

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?

Accepted Answer

Colt

Answer

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:

Accepted Answer

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

Answer

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?

Accepted Answer

Ninhydrin

Answer

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?

Accepted Answer

Likelihood Ratio (LR)

Answer

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.

(FBI) Federal Bureau of Investigation Certified Marksman Practice Test

(FBI) Federal Bureau of Investigation Certified Marksman Practice Test

FBI Forensic Science & Analysis 2