FDC Evidence Collection & Preservation 2 — Questions and Answers
Question 1: Which packaging material is MOST appropriate for storing wet biological evidence such as bloodstained clothing?
- Airtight plastic bag to prevent evaporation
- Paper bag to allow moisture to escape and prevent mold (Correct answer)
- Aluminum foil sealed with tape
- Vacuum-sealed polyethylene pouch
Correct answer: Paper bag to allow moisture to escape and prevent mold
Wet biological evidence must be packaged in paper (not plastic) to allow airflow that prevents mold and bacterial overgrowth that would degrade DNA.
Question 2: A chain of custody document for DNA evidence MUST record which of the following each time the evidence changes hands?
- The DNA profile obtained from the evidence
- The identity of each person handling it, date, time, and reason for transfer (Correct answer)
- The storage temperature at time of transfer
- The case detective's approval signature only
Correct answer: The identity of each person handling it, date, time, and reason for transfer
Chain of custody requires documenting who handled the evidence, when, and why at every transfer to demonstrate unbroken accountability.
Question 3: When collecting a buccal swab reference sample, the collector should ensure the donor has NOT eaten, drunk, or smoked for at least how long prior to collection?
- 5 minutes
- 20 minutes
- 30 minutes (Correct answer)
- 2 hours
Correct answer: 30 minutes
A 30-minute abstention period before buccal swabbing reduces the risk of food particles and foreign DNA contaminating the reference sample.
Question 4: Which of the following is the correct sequence for collecting multiple swabs from the same stain on a surface?
- Dry swab first, then wet swab to resuspend residual material
- Wet swab first to rehydrate cells, then dry swab to absorb the released material (Correct answer)
- Two wet swabs simultaneously for redundancy
- Single dry swab only to avoid dilution
Correct answer: Wet swab first to rehydrate cells, then dry swab to absorb the released material
The wet-dry (or double-swab) technique uses a wet swab to rehydrate the stain and a dry swab to absorb the lifted cellular material, maximizing DNA yield.
Question 5: Luminol testing at a crime scene can affect subsequent DNA analysis primarily because it:
- Permanently destroys nuclear DNA in bloodstains
- May inhibit PCR amplification when luminol residue is present in extracts (Correct answer)
- Converts hemoglobin into a non-typeable form
- Renders the sample inadmissible without additional authentication
Correct answer: May inhibit PCR amplification when luminol residue is present in extracts
Luminol contains hydrogen peroxide and sodium hydroxide that can carry over into extracts and inhibit PCR, reducing or eliminating DNA typing success.
Question 6: For long-term archival storage of dried DNA extracts, the recommended storage condition is:
- 4°C refrigerator in aqueous solution
- -20°C freezer in TE buffer
- -80°C ultra-low freezer, dried or in TE buffer (Correct answer)
- Room temperature in silica gel desiccant pouches
Correct answer: -80°C ultra-low freezer, dried or in TE buffer
Long-term DNA archival storage at -80°C minimizes hydrolytic and oxidative degradation, preserving sample integrity for decades.
Question 7: When a forensic examiner discovers that a sealed evidence package has been tampered with before analysis, the FIRST required action is to:
- Open the package and proceed with analysis to preserve findings
- Discard the evidence as it is no longer admissible
- Document the breach and notify the submitting agency and chain of custody custodian (Correct answer)
- Re-seal the package and proceed without notation
Correct answer: Document the breach and notify the submitting agency and chain of custody custodian
A tampered seal must be documented immediately and reported to maintain chain of custody integrity and allow legal and administrative review.
FDC Evidence Collection & Preservation 2
Which packaging material is MOST appropriate for storing wet biological evidence such as bloodstained clothing?