ETC Trace Evidence 2 — Questions and Answers
Question 1: Which analytical technique is most commonly used to determine the chemical composition and polymer type of fiber evidence?
- X-ray diffraction (XRD)
- Fourier transform infrared spectroscopy (FTIR) (Correct answer)
- Gas chromatography alone
- Atomic absorption spectroscopy
Correct answer: Fourier transform infrared spectroscopy (FTIR)
FTIR produces a unique infrared absorption spectrum that acts as a chemical fingerprint for fiber polymers, allowing examiners to identify and compare fiber types.
Question 2: When collecting soil samples as comparison trace evidence, what is the correct procedure?
- Collect only from the exact location where the suspect stood
- Take a single large sample from near the victim
- Collect samples from multiple locations including control areas away from the scene (Correct answer)
- Skip soil collection if the ground is dry
Correct answer: Collect samples from multiple locations including control areas away from the scene
Collecting samples from multiple locations — including known control areas — allows forensic geologists to compare the questioned soil to reference samples and assess significance.
Question 3: What microscopic index value helps differentiate human hair from most animal hair?
- Cortical cell ratio
- Pigment density index
- Medullary index (Correct answer)
- Cuticle scale count
Correct answer: Medullary index
The medullary index (medulla diameter ÷ total hair diameter) is typically less than 1/3 in human hair and greater than 1/2 in most animal hairs, making it a key distinguishing feature.
Question 4: What is gunshot residue (GSR) primarily composed of, and why is it significant as trace evidence?
- Carbon and nitrogen compounds indicating smokeless powder
- Lead, barium, and antimony particles unique to firearm discharge (Correct answer)
- Iron oxide and copper from the bullet jacket only
- Nitrates and nitrites from the propellant gases
Correct answer: Lead, barium, and antimony particles unique to firearm discharge
The unique tri-element combination of lead, barium, and antimony in fused spherical particles is characteristic of primer discharge and is detectable on hands, clothing, and surfaces near a fired weapon.
Question 5: Which tool is most appropriate for collecting dry, loose trace evidence such as glass fragments or paint chips from a surface?
- Moistened cotton swab
- Adhesive tape roller
- Forceps or fine-tipped tweezers (Correct answer)
- Stiff-bristle brush
Correct answer: Forceps or fine-tipped tweezers
Forceps or tweezers allow the technician to pick up individual fragments with precision, avoiding contamination and maintaining the integrity of each piece of trace evidence.
Question 6: What forensic value do glass fracture patterns provide in a crime scene investigation?
- They permanently trap DNA from the person who broke the glass
- They can indicate the direction and sequence of multiple impacts (Correct answer)
- They reveal the exact weight of the object used to break them
- They identify the specific brand of glass manufacturer
Correct answer: They can indicate the direction and sequence of multiple impacts
Radial and concentric fracture lines, along with stress marks on fracture edges, can be used to determine the direction of impact force and the sequence in which multiple breaks occurred.
Question 7: In trace evidence searches, which area of the crime scene should generally be examined first?
- The center of the crime scene where the main event occurred
- Entry and exit pathways only
- The perimeter boundary of the scene
- The most volatile area likely to be disturbed or where evidence could be lost (Correct answer)
Correct answer: The most volatile area likely to be disturbed or where evidence could be lost
Volatile areas — those subject to weather, foot traffic, or environmental change — should be processed first to preserve fragile trace evidence before it is displaced or destroyed.
ETC Trace Evidence 2
Which analytical technique is most commonly used to determine the chemical composition and polymer type of fiber evidence?