Chapter 24 — Self-Check Quiz

24 questions: multiple choice and short answer. Try them closed-book. The answer key is in the collapsed block at the bottom.

Multiple choice

1. The diagnostic particle of primer residue most commonly contains which three elements fused together? - A. Iron, copper, zinc - B. Lead, barium, antimony - C. Sodium, calcium, potassium - D. Carbon, nitrogen, oxygen

2. Finding GSR particles on a person's hands establishes: - A. That the person fired a gun - B. That GSR is present on the person — not, by itself, that the person fired a weapon - C. The exact firearm used - D. The time of the shooting

3. The instrument used to confirm a GSR particle by both its shape and its elemental composition is: - A. A comparison microscope - B. A polygraph - C. The scanning electron microscope with energy-dispersive X-ray analysis (SEM-EDX) - D. A refractometer

4. Why is "lead present on the swab" a weak GSR finding? - A. Lead is never found in primer residue - B. Lead, barium, and antimony are common in everyday non-firearm sources individually; what is rare is the three fused in one particle of the right shape - C. Lead cannot be measured accurately - D. The test is illegal

5. Secondary transfer of GSR means: - A. GSR can only be deposited by the shooter - B. A non-shooter can acquire GSR by contact with a contaminated person, surface, or environment (e.g., a patrol car) - C. GSR doubles in quantity over time - D. GSR is impossible to detect after one hour

6. A negative GSR result on a person sampled many hours after a shooting: - A. Proves the person did not fire a weapon - B. Proves the person did fire a weapon - C. Proves little — particles are lost within hours, so absence is consistent with both firing and not firing - D. Is impossible to obtain

7. In a paint-layer comparison, the probabilistic weight of the association lives primarily in: - A. Any single layer - B. The color of the basecoat alone - C. The number, sequence, and composition of the layers taken together - D. The thickness of the clearcoat only

8. A multi-layer paint match that includes an unusual aftermarket repaint is stronger than a single common-layer match because: - A. Repainted cars are always guilty - B. Each independent matching feature multiplies the rarity, making a coincidental common source less likely - C. Aftermarket paint cannot be analyzed - D. The clearcoat is always unique

9. A physical (fracture) fit between a paint chip and a damaged vehicle area is significant because: - A. It is weaker than a layer comparison - B. It reconstructs a unique break and approaches individualization, unlike compositional class evidence - C. It proves who was driving - D. It dates the collision

10. The refractive index of glass measures: - A. The color of the glass - B. How much the material bends (slows) light passing through it - C. The weight of the fragment - D. The age of the window

11. A difference in refractive index between two glass fragments: - A. Is meaningless - B. Excludes a common source — they cannot have come from the same glass - C. Proves a common source - D. Individualizes the window

12. Two glass fragments with matching refractive index are best described as: - A. Proven to share a source - B. Consistent with a common source, but float glass of this type is mass-produced, so not individualized - C. From the same window for certain - D. Worthless evidence

13. When a pane is broken by an impact, radial cracks: - A. Form rings around the impact point - B. Run outward from the point of impact like spokes - C. Do not form in real glass - D. Indicate the time of breakage

14. Glass fracture analysis can determine which side a force came from, which tells you: - A. Who broke the glass - B. The mechanics/direction of the break (e.g., broken from outside vs. inside) — not the identity of the breaker - C. The exact tool used - D. The motive

15. Soil is potentially powerful class evidence because: - A. It is always unique to one spot - B. It is a composite of many independent properties (color, mineralogy, texture, pollen, chemistry) that each add a comparison point - C. It cannot be analyzed instrumentally - D. It individualizes a location like DNA

16. The single most important collection step that determines whether soil evidence will mean anything is: - A. Taking one sample from the center of the scene - B. Collecting multiple known samples of the distinctive spot and the surrounding background, so distinctiveness can be assessed against a baseline - C. Drying the sample in plastic - D. Refusing to take control samples

17. In the cold case, the soil on Roy Keller's boots most defensibly establishes that: - A. Keller killed Diallo - B. Keller was at the scene at the time of the fire - C. Keller's boots (and so, reasonably, Keller) were in the cabin's distinctive environment — a place-level association, not a time or a culprit - D. A crime was committed

18. The "strongly supports" (rather than merely "consistent with") strength of the cold-case soil association is earned specifically by: - A. The detective's confidence - B. The control samples showing the matched mineral/pollen combination is uncommon in the surrounding county - C. The number of boots seized - D. The weather on the day of the fire

19. The single most dangerous word in this chapter, because it launders a class association into a perceived certainty, is: - A. "Excludes" - B. "Match" - C. "Consistent" - D. "Indistinguishable"

20. An examiner pressed for a numerical frequency for a soil association, with no validated population database, should: - A. Invent a plausible number like "one in a million" - B. Refuse to fabricate a statistic and instead explain why the association is weak or strong (distinctiveness, number of independent features) - C. Say the soil individualizes the scene - D. Decline to testify at all

Short answer

21. Explain in two sentences why "GSR on the suspect's hands" is consistent with several explanations other than the suspect firing a weapon. Name at least two of those explanations.

22. Why does the strength of a class association (in paint, glass, or soil) scale with the rarity of the match? State the two factors that drive rarity.

23. In the cold case, explain how the negative GSR result, the no gunshot wound autopsy finding (Chapter 11), and the red-herring cartridge case (Chapter 15) sit together consistently.

24. Write one sentence an honest expert could say on the stand about the Mill Creek soil-on-the-boots evidence, and one sentence that would overstate it.

Answer key (click to expand) **Multiple choice:** 1-B · 2-B · 3-C · 4-B · 5-B · 6-C · 7-C · 8-B · 9-B · 10-B · 11-B · 12-B · 13-B · 14-B · 15-B · 16-B · 17-C · 18-B · 19-B · 20-B **Short answer (model points):** **21.** GSR particles are tiny, light, and transfer easily; their presence records only that residue reached the surface, not how. Other explanations include: contact transfer from a person or surface that had GSR (secondary/tertiary transfer); occupational/environmental background (police, range workers, hunters); and police-transport or booking-area contamination (patrol cars, holding cells, an arresting officer's hands). The honest conclusion is "particles were present," not "the suspect fired a weapon." **22.** A class match means the questioned and known items share features but the features are shared by a *group*; the strength of the association is the *improbability that the match arose by coincidence*. Rarity drives that improbability, and rarity has two factors: **distinctiveness** (how unusual the matched feature is — a rare paint, an uncommon mineral) and **independence/number** (how many independent properties match, since the chance of sharing all of them by coincidence is the product of the individual chances). **23.** No soot in the airways and a blunt-force skull fracture established that Diallo died of blunt-force trauma with *no gunshot wound* (Chapter 11). The stray cartridge case was shown to be a red herring, unrelated to the manner of death (Chapter 15). A negative GSR result — no primer-residue particles where a shooting would have produced them — is exactly what one expects when there was no shooting. All three findings agree: no one was shot. (Note: a negative GSR proves little *alone*, per §24.1, but here it merely *corroborates* a manner of death already established by the body.) **24.** **Honest:** "The soil on the boots is consistent with, and — given that the controls show the matched mineral and pollen combination to be uncommon in the region — strongly supports, the boots having been in the cabin's distinctive environment; it does not establish when the soil was acquired or that any crime was committed." **Overstated:** "The soil proves the defendant was at the murder scene at the time of the killing." (Or: "The soil proves he did it.")